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/tasks.py

@@ -36,7 +36,15 @@ def render(db: Session, frame: Frame, widget: Widget, target_w: int, target_h: i
     signature regardless of which ones actually care."""
     tasks = get_or_refresh_tasks_for_widget(db, frame, widget)
     cfg = db.get(TaskWidgetConfig, widget.id)
-    return _build_tasks(tasks, target_w, target_h, frame.palette_rgb, cfg.name or "Tasks")
+    title = cfg.name or "Tasks"
+    if 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.
+        from .. import html_render
+
+        return html_render.build_tasks(tasks, target_w, target_h, frame.palette_rgb, title)
+    return _build_tasks(tasks, target_w, target_h, frame.palette_rgb, title)
 
 
 ACTIONS: dict = {}