Roll out "modern" HTML/CSS render style to every widget except photos

Extends weather's experimental Chromium+Jinja2 render style to battery,
text, tasks, static image, whiteboard, and calendar (all four view
modes -- agenda/today_tomorrow/week/month), and gives the photos widget
its own genuinely independent palette + dithering strength.

Photos: Frame.photo_palette_rgb/photo_dither_strength (mirroring the
existing palette_rgb/dither_strength), with a second "Photos
configuration" card in Advanced Configuration. widgets/photos.py's
render() quantizes itself against these before returning -- no
render_panel changes needed, since photos is the only widget that
genuinely needs a different reference palette and can carry that
itself, the same way modern-style widgets already self-dither via
ordered_dither.

Battery/text/tasks/static image/whiteboard: same render_style pattern
weather established (render_style column, html_render.py build
function, Jinja2 template, dialog toggle). Static image/whiteboard get
their first-ever visual chrome (a rounded-corner shadowed card,
shared framed_image.html.jinja) since classic draws them with zero
frame at all. Fixed the same "preview endpoint bypasses render_style"
bug weather originally shipped with, for tasks/static/whiteboard/
calendar's preview endpoints.

Calendar: own module (app/calendar_html_render.py, mirroring
calendar_render.py's separation from the simpler widgets) covering all
four view modes, not just agenda -- reuses calendar_render's own
private helpers so event colors/times/weather/month-grid math match
classic exactly. Found and fixed two real cross-day layout bugs along
the way: a per-day header height that varied based on whether that
specific day had a weather entry (misaligning where every other day's
event rows started across the week/month grid), and regular-weight
small text being fragile under Bayer ordered dithering (out-of-month
day numbers degraded into unrecognizable speckle) -- fixed by using
bold everywhere and de-emphasizing via size instead of weight/gray,
since gray text has the same dithering fragility this project's PIL
renderers already avoid for exactly this reason.

Migrations 32-38 (Frame's two new columns, then one render_style column
per widget config table). 452 tests passing, including new dispatch/
migration coverage per widget type and a dedicated photos test proving
photo_palette_rgb produces genuinely independent quantization from the
frame's main palette_rgb.

server/app/calendar_html_render.py

@@ -0,0 +1,291 @@
+"""Calendar widget's "modern" render style -- all four view modes
+(agenda/today_tomorrow/week/month), mirroring calendar_render.py's own
+_build dispatch shape exactly so app/widgets/calendar.py and the
+calendar preview endpoint can call either module identically. Kept in
+its own module rather than joining app/html_render.py's other build_*
+functions, mirroring calendar_render.py's own separation from the
+simpler widgets (calendar is the one case where html_render.py growing
+a 5th unrelated builder starts to hurt readability).
+
+Reuses calendar_render's own private helpers (_events_on_day/_event_
+colors/_event_start/_fmt_time/_weather_for_day/_month_view_fits/
+_add_months) so a modern-style view's event list/colors/times/weather/
+month-grid math match the classic renderer's data exactly -- only the
+drawing differs, same relationship weather's build_current/build_daily
+have with weather_render.py."""
+
+from __future__ import annotations
+
+import calendar as calendar_module
+from datetime import date, datetime, timedelta
+from zoneinfo import ZoneInfo
+
+from PIL import Image
+
+from . import html_render, panel_style
+from .calendar_render import (
+    MARGIN,
+    WEEKDAY_NAMES,
+    _add_months,
+    _event_colors,
+    _event_start,
+    _events_on_day,
+    _fmt_time,
+    _month_view_fits,
+    _weather_for_day,
+)
+
+
+def _weather_row(weather_cities, day, units) -> list[dict]:
+    entries = _weather_for_day(weather_cities, day)
+    return [
+        {"emoji": html_render.CATEGORY_EMOJI.get(e["category"], ""), "high": round(e["high"]), "low": round(e["low"])}
+        for e in entries
+    ]
+
+
+def _day_section_data(day: date, events: list[dict], tz: ZoneInfo, palette_rgb, weather_cities,
+                      weather_units: str, owners_seen: list[str], rows_avail_h: int, row_h: int) -> dict:
+    """One day's {header, weather_entries, rows, more_count} -- shared by
+    build_agenda/build_today_tomorrow/build_week's vertical layout, same
+    reuse relationship calendar_render._draw_agenda_day has with
+    _build_agenda/_build_today_tomorrow. `rows_avail_h` is the *rows*
+    area's own pixel budget only -- the caller has already reserved a
+    separate, uniform header_h (which is where weather actually renders,
+    see the day-header macro) for every section, so this function
+    doesn't need to account for weather space itself."""
+    header = day.strftime("%A, %B ") + str(day.day)
+    weather_entries = _weather_row(weather_cities, day, weather_units)
+    max_rows = max(0, rows_avail_h // row_h)
+
+    day_events = _events_on_day(events, day, tz)
+    rows = []
+    for event in day_events[:max_rows]:
+        colors = _event_colors(event, owners_seen, palette_rgb)
+        time_str = "All day" if event["all_day"] else _fmt_time(_event_start(event, tz))
+        rows.append({"colors": [html_render._rgb_to_hex(c) for c in colors], "time": time_str,
+                     "summary": event["summary"]})
+    return {"header": header, "weather_entries": weather_entries, "rows": rows,
+            "more_count": max(0, len(day_events) - max_rows)}
+
+
+def build_agenda(events: list[dict], browse_offset: int, target_w: int, target_h: int, tz: ZoneInfo,
+                 palette_rgb: list | None = None, weather_cities: list[dict] | None = None,
+                 weather_units: str = "fahrenheit") -> Image.Image:
+    """HTML/CSS-rendered analogue of calendar_render._build_agenda."""
+    day = datetime.now(tz).date() + timedelta(days=browse_offset)
+    title_size = max(14, min(target_w, target_h) // 12)
+    body_size = max(11, min(target_w, target_h) // 20)
+    weather_size = max(10, body_size - 2)
+    row_h = body_size + 14
+    unit_suffix = "F" if weather_units == "fahrenheit" else "C"
+
+    # Single day -- no cross-section alignment concern, so header_h can
+    # simply reflect whether THIS day actually has weather (unlike
+    # build_today_tomorrow/build_week's vertical layout, which must
+    # reserve the same header_h for every stacked section regardless).
+    has_weather = bool(_weather_row(weather_cities, day, weather_units))
+    header_h = title_size + 24 + ((weather_size + 12) if has_weather else 0)
+
+    owners_seen: list[str] = []
+    data = _day_section_data(day, events, tz, palette_rgb, weather_cities, weather_units, owners_seen,
+                             target_h - header_h - MARGIN, row_h)
+
+    accent = html_render._rgb_to_hex(panel_style.ink(palette_rgb, panel_style.THEME_CALENDAR))
+    template = html_render._jinja_env.get_template("calendar_agenda.html.jinja")
+    html = template.render(
+        w=target_w, h=target_h, gutter=panel_style.GUTTER, radius=panel_style.CARD_RADIUS,
+        font_dir=str(html_render._FONT_DIR), header=data["header"], title_size=title_size, header_h=header_h,
+        accent_start=accent, accent_end=accent, weather_entries=data["weather_entries"],
+        weather_size=weather_size, unit_suffix=unit_suffix, rows=data["rows"],
+        more_count=data["more_count"], row_h=row_h, body_size=body_size,
+    )
+    rendered = html_render.render_html_to_image(html, target_w, target_h)
+    return html_render.ordered_dither(rendered, palette_rgb)
+
+
+def build_today_tomorrow(events: list[dict], browse_offset: int, target_w: int, target_h: int, tz: ZoneInfo,
+                         palette_rgb: list | None = None, weather_cities: list[dict] | None = None,
+                         weather_units: str = "fahrenheit") -> Image.Image:
+    """HTML/CSS-rendered analogue of calendar_render._build_today_tomorrow
+    -- two day-sections stacked (see _day_section_data)."""
+    start_day = datetime.now(tz).date() + timedelta(days=browse_offset)
+    section_h = target_h // 2
+    title_size = max(13, section_h // 8)
+    body_size = max(10, min(target_w, target_h) // 26)
+    weather_size = max(9, body_size - 2)
+    row_h = body_size + 12
+    unit_suffix = "F" if weather_units == "fahrenheit" else "C"
+
+    day_dates = [start_day + timedelta(days=i) for i in range(2)]
+    # Uniform across both stacked sections regardless of which day(s)
+    # actually have weather -- see _day_section_data's own docstring for
+    # why a per-day header height misaligns where rows start.
+    any_weather = any(_weather_row(weather_cities, d, weather_units) for d in day_dates)
+    header_h = title_size + 16 + ((weather_size + 10) if any_weather else 0)
+
+    owners_seen: list[str] = []
+    days = [
+        _day_section_data(d, events, tz, palette_rgb, weather_cities, weather_units, owners_seen,
+                          section_h - header_h, row_h)
+        for d in day_dates
+    ]
+
+    accent = html_render._rgb_to_hex(panel_style.ink(palette_rgb, panel_style.THEME_CALENDAR))
+    template = html_render._jinja_env.get_template("calendar_today_tomorrow.html.jinja")
+    html = template.render(
+        w=target_w, h=target_h, gutter=panel_style.GUTTER, radius=panel_style.CARD_RADIUS,
+        font_dir=str(html_render._FONT_DIR), days=days, title_size=title_size, header_h=header_h,
+        accent_start=accent, accent_end=accent, weather_size=weather_size, unit_suffix=unit_suffix,
+        row_h=row_h, body_size=body_size,
+    )
+    rendered = html_render.render_html_to_image(html, target_w, target_h)
+    return html_render.ordered_dither(rendered, palette_rgb)
+
+
+def build_week(events: list[dict], browse_offset: int, target_w: int, target_h: int, tz: ZoneInfo,
+              week_start: int, palette_rgb: list | None = None, weather_cities: list[dict] | None = None,
+              weather_units: str = "fahrenheit", days: int = 7, layout: str = "horizontal",
+              start_offset: int = 0) -> Image.Image:
+    """HTML/CSS-rendered analogue of calendar_render._build_week -- both
+    the vertical (stacked day-sections, reusing build_today_tomorrow's
+    template with an arbitrary day count) and horizontal (side-by-side
+    columns) layouts."""
+    today = datetime.now(tz).date()
+    if days == 7:
+        days_since_start = (today.weekday() - week_start) % 7
+        week_first_day = today - timedelta(days=days_since_start) + timedelta(days=days * browse_offset)
+    else:
+        week_first_day = today + timedelta(days=start_offset) + timedelta(days=days * browse_offset)
+    unit_suffix = "F" if weather_units == "fahrenheit" else "C"
+    accent = html_render._rgb_to_hex(panel_style.ink(palette_rgb, panel_style.THEME_CALENDAR))
+    owners_seen: list[str] = []
+
+    if layout == "vertical":
+        section_h = target_h // days
+        title_size = max(11, min(20, section_h // 6))
+        body_size = max(9, min(target_w, target_h) // (18 + days))
+        weather_size = max(8, body_size - 2)
+        row_h = body_size + 10
+        day_dates = [week_first_day + timedelta(days=i) for i in range(days)]
+        # Uniform across all `days` stacked sections -- see
+        # _day_section_data's own docstring for why a per-day header
+        # height misaligns where rows start.
+        any_weather = any(_weather_row(weather_cities, d, weather_units) for d in day_dates)
+        header_h = title_size + 12 + ((weather_size + 8) if any_weather else 0)
+        day_sections = [
+            _day_section_data(d, events, tz, palette_rgb, weather_cities, weather_units, owners_seen,
+                             section_h - header_h, row_h)
+            for d in day_dates
+        ]
+        template = html_render._jinja_env.get_template("calendar_today_tomorrow.html.jinja")
+        html = template.render(
+            w=target_w, h=target_h, gutter=panel_style.GUTTER, radius=panel_style.CARD_RADIUS,
+            font_dir=str(html_render._FONT_DIR), days=day_sections, title_size=title_size, header_h=header_h,
+            accent_start=accent, accent_end=accent, weather_size=weather_size, unit_suffix=unit_suffix,
+            row_h=row_h, body_size=body_size,
+        )
+        rendered = html_render.render_html_to_image(html, target_w, target_h)
+        return html_render.ordered_dither(rendered, palette_rgb)
+
+    header_size = max(10, min(16, (target_w // days) // 6))
+    chip_size = max(9, header_size - 3)
+    weather_size = max(8, chip_size - 1)
+    col_w = max(1, (target_w - panel_style.GUTTER * 2) // days)
+    row_h = chip_size + 8
+    # Reserve weather-line room in every column's header uniformly
+    # (whether or not THIS specific day has a cached forecast) -- a
+    # per-column height that depends on that day's own data would
+    # misalign where each column's event rows start across the week
+    # grid the moment any single day lacks a forecast entry.
+    header_h = header_size + 22 + (weather_size + 6 if weather_cities else 0)
+    max_rows = max(0, (target_h - panel_style.GUTTER * 2 - header_h) // row_h)
+
+    cols = []
+    for i in range(days):
+        day = week_first_day + timedelta(days=i)
+        label = day.strftime("%a %-d") if day != today else f"★ {day.strftime('%a %-d')}"
+        weather_entries = _weather_row(weather_cities, day, weather_units)
+        day_events = _events_on_day(events, day, tz)
+        rows = []
+        for event in day_events[:max_rows]:
+            color = html_render._rgb_to_hex(_event_colors(event, owners_seen, palette_rgb)[0])
+            summary = event["summary"] if event["all_day"] else f"{_fmt_time(_event_start(event, tz))[:-3]} {event['summary']}"
+            rows.append({"color": color, "summary": summary})
+        cols.append({
+            "label": label, "weather": weather_entries[0] if weather_entries else None,
+            "rows": rows, "more_count": max(0, len(day_events) - max_rows),
+        })
+
+    template = html_render._jinja_env.get_template("calendar_week_horizontal.html.jinja")
+    html = template.render(
+        w=target_w, h=target_h, gutter=panel_style.GUTTER, radius=panel_style.CARD_RADIUS,
+        font_dir=str(html_render._FONT_DIR), cols=cols, header_size=header_size, chip_size=chip_size,
+        header_h=header_h, weather_size=weather_size, unit_suffix=unit_suffix, accent_start=accent, accent_end=accent,
+    )
+    rendered = html_render.render_html_to_image(html, target_w, target_h)
+    return html_render.ordered_dither(rendered, palette_rgb)
+
+
+def build_month(events: list[dict], browse_offset: int, target_w: int, target_h: int, tz: ZoneInfo,
+               week_start: int, palette_rgb: list | None = None) -> Image.Image:
+    """HTML/CSS-rendered analogue of calendar_render._build_month --
+    density dots per day, not literal event text, same reasoning as the
+    classic renderer (real text at typical month-cell size is close to
+    unreadable on a 6-color dithered e-ink panel)."""
+    today = datetime.now(tz).date()
+    target_month = _add_months(date(today.year, today.month, 1), browse_offset)
+    weeks_dates = list(
+        calendar_module.Calendar(firstweekday=week_start).monthdatescalendar(target_month.year, target_month.month)
+    )
+    day_names = [n[:3] for n in (WEEKDAY_NAMES[week_start:] + WEEKDAY_NAMES[:week_start])]
+
+    header_size = max(11, min(16, target_h // 30))
+    day_size = max(10, min(15, target_w // 55))
+    dot_size = max(4, day_size // 2)
+    accent = html_render._rgb_to_hex(panel_style.ink(palette_rgb, panel_style.THEME_CALENDAR))
+
+    owners_seen: list[str] = []
+    weeks = []
+    for week in weeks_dates:
+        row = []
+        for day in week:
+            day_events = _events_on_day(events, day, tz)
+            dots = [html_render._rgb_to_hex(_event_colors(e, owners_seen, palette_rgb)[0]) for e in day_events[:4]]
+            row.append({
+                "day_num": day.day, "in_month": day.month == target_month.month,
+                "is_today": day == today, "dots": dots, "more_count": max(0, len(day_events) - 4),
+            })
+        weeks.append(row)
+
+    template = html_render._jinja_env.get_template("calendar_month.html.jinja")
+    html = template.render(
+        w=target_w, h=target_h, gutter=panel_style.GUTTER, radius=panel_style.CARD_RADIUS,
+        font_dir=str(html_render._FONT_DIR), day_names=day_names, weeks=weeks,
+        header_size=header_size, day_size=day_size, dot_size=dot_size, accent_start=accent,
+    )
+    rendered = html_render.render_html_to_image(html, target_w, target_h)
+    return html_render.ordered_dither(rendered, palette_rgb)
+
+
+def build(events: list[dict], view: str, browse_offset: int, target_w: int, target_h: int, tz: ZoneInfo,
+         week_start: int, palette_rgb: list | None = None, weather_cities: list[dict] | None = None,
+         weather_units: str = "fahrenheit", week_days: int = 7, week_layout: str = "horizontal",
+         week_start_offset: int = 0) -> Image.Image:
+    """Dispatches to the right build_* -- mirrors calendar_render._build's
+    exact "month falls back to agenda when it doesn't fit" resolution, so
+    a narrow month-mode widget set to modern style still gets a sensible
+    modern view instead of erroring or silently reverting to classic."""
+    effective_view = view
+    if view == "month" and not _month_view_fits(target_w, target_h):
+        effective_view = "agenda"
+
+    if effective_view == "agenda":
+        return build_agenda(events, browse_offset, target_w, target_h, tz, palette_rgb, weather_cities, weather_units)
+    if effective_view == "today_tomorrow":
+        return build_today_tomorrow(events, browse_offset, target_w, target_h, tz, palette_rgb, weather_cities,
+                                    weather_units)
+    if effective_view == "week":
+        return build_week(events, browse_offset, target_w, target_h, tz, week_start, palette_rgb, weather_cities,
+                          weather_units, week_days, week_layout, week_start_offset)
+    return build_month(events, browse_offset, target_w, target_h, tz, week_start, palette_rgb)