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/tests/test_migrations.py

@@ -94,6 +94,16 @@ def test_expected_columns_exist_on_current_schema():
     assert {"hold_duration_ms", "next_hold_action", "back_hold_action", "last_cycled_layout_id"} <= frame_columns
     assert {"last_displayed_image", "last_displayed_at"} <= frame_columns  # migration 30
     assert "render_style" in weather_widget_columns  # migration 31
+    assert {"photo_palette_rgb", "photo_dither_strength"} <= frame_columns  # migration 32
+    assert "render_style" in battery_widget_columns  # migration 33
+    assert "render_style" in text_widget_columns  # migration 34
+    assert "render_style" in task_widget_columns  # migration 35
+    static_widget_columns = {c["name"] for c in inspector.get_columns("static_widget_configs")}
+    assert "render_style" in static_widget_columns  # migration 36
+    whiteboard_widget_columns = {c["name"] for c in inspector.get_columns("whiteboard_widget_configs")}
+    assert "render_style" in whiteboard_widget_columns  # migration 37
+    calendar_widget_columns = {c["name"] for c in inspector.get_columns("calendar_widget_configs")}
+    assert "render_style" in calendar_widget_columns  # migration 38
 
 
 # --- widget system backfill (migration 16 + _ensure_widgets_backfilled) ---