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/widgets/battery.py

@@ -60,6 +60,21 @@ def _format_age(as_of: float) -> str:
     return f"{round(delta / 86400)}d ago"
 
 
+def _lines_for(mode: str, frame: Frame, db: Session) -> list[str]:
+    """The 0-2 caption lines "detailed" mode shows below the percent --
+    shared by both render styles so the estimate/age formatting only
+    lives in one place."""
+    if mode != "detailed":
+        return []
+    lines = []
+    estimate_s = battery_estimate_s(frame, db)
+    if estimate_s is not None:
+        lines.append(_format_estimate(estimate_s))
+    if frame.battery_as_of:
+        lines.append(f"Reported {_format_age(frame.battery_as_of)}")
+    return lines
+
+
 def render(db: Session, frame: Frame, widget: Widget, target_w: int, target_h: int,
           is_normal_wake: bool = True) -> Image.Image:
     """is_normal_wake is unused -- see app/widgets/whiteboard.py's
@@ -72,6 +87,16 @@ def render(db: Session, frame: Frame, widget: Widget, target_w: int, target_h: i
     cfg = db.get(BatteryWidgetConfig, widget.id)
     mode = cfg.mode if cfg else "detailed"
     palette_rgb = frame.palette_rgb
+    lines = _lines_for(mode, frame, db)
+
+    if cfg and cfg.render_style == "modern":
+        # Local import: html_render pulls in Playwright, a real headless-
+        # Chromium dependency -- every other widget type, and this one's
+        # own classic path, should never pay for it (same reasoning as
+        # image_pipeline.render_placeholder's local `import qrcode`).
+        from .. import html_render
+
+        return html_render.build_battery(percent, lines, target_w, target_h, palette_rgb)
 
     img, draw, (cx0, cy0, cw, ch) = panel_style.card_canvas(target_w, target_h)
     cx = cx0 + cw // 2
@@ -92,23 +117,15 @@ def render(db: Session, frame: Frame, widget: Widget, target_w: int, target_h: i
     draw_text(img, (cx - (bbox[2] - bbox[0]) // 2, pct_y), pct_text, pct_font,
              panel_style.battery_fill_color(percent, palette_rgb))
 
-    if mode == "detailed":
-        lines = []
-        estimate_s = battery_estimate_s(frame, db)
-        if estimate_s is not None:
-            lines.append(_format_estimate(estimate_s))
-        if frame.battery_as_of:
-            lines.append(f"Reported {_format_age(frame.battery_as_of)}")
-
-        small_font_size = max(11, pct_font_size // 3)
-        small_font = panel_style.font_regular(small_font_size)
-        y = pct_y + pct_font_size + 12
-        for line in lines:
-            if y + small_font_size > cy0 + ch - 4:
-                break
-            lbbox = draw.textbbox((0, 0), line, font=small_font)
-            draw_text(img, (cx - (lbbox[2] - lbbox[0]) // 2, y), line, small_font)
-            y += small_font_size + 6
+    small_font_size = max(11, pct_font_size // 3)
+    small_font = panel_style.font_regular(small_font_size)
+    y = pct_y + pct_font_size + 12
+    for line in lines:
+        if y + small_font_size > cy0 + ch - 4:
+            break
+        lbbox = draw.textbbox((0, 0), line, font=small_font)
+        draw_text(img, (cx - (lbbox[2] - lbbox[0]) // 2, y), line, small_font)
+        y += small_font_size + 6
 
     return img