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_widgets_battery.py

@@ -7,17 +7,19 @@ from __future__ import annotations
 
 import time
 
-from app import widgets
+from PIL import Image
+
+from app import html_render, widgets
 from app.models import BatteryWidgetConfig, Frame, Widget
 
 
-def _make_widget(db_session, mode="detailed") -> tuple[Frame, Widget]:
+def _make_widget(db_session, mode="detailed", render_style="classic") -> tuple[Frame, Widget]:
     frame = db_session.get(Frame, 1)
     widget = Widget(frame_id=frame.id, widget_type="battery", x=0, y=0, w=1, h=1,
                     sort_order=0, created_at=time.time())
     db_session.add(widget)
     db_session.flush()
-    db_session.add(BatteryWidgetConfig(widget_id=widget.id, mode=mode))
+    db_session.add(BatteryWidgetConfig(widget_id=widget.id, mode=mode, render_style=render_style))
     db_session.commit()
     return frame, widget
 
@@ -81,3 +83,19 @@ def test_no_button_actions():
     advance/back/check."""
     assert widgets.battery.ACTIONS == {}
     assert widgets.battery.ACTION_LABELS == {}
+
+
+def test_render_modern_style(db_session, monkeypatch):
+    frame, widget = _make_widget(db_session, render_style="modern")
+    frame.battery_percent = 42
+    frame.battery_as_of = time.time()
+    db_session.commit()
+
+    def _stub(html, target_w, target_h):
+        return Image.new("RGB", (target_w, target_h), (255, 255, 255))
+
+    monkeypatch.setattr(html_render, "render_html_to_image", _stub)
+
+    img = widgets.battery.render(db_session, frame, widget, 300, 200)
+    assert img.size == (300, 200)
+    assert img.mode == "RGB"