Widget system Phase 2: full cutover to widget-based rendering

device.py's mode-keyed dispatch is replaced by a real compositor:
load a frame's widgets, compute pixel rects via app/grid.py, render
each through its widget module, and composite with render_panel.
Physical NEXT/BACK buttons now execute each frame's assigned
FrameButtonAction rows instead of one hardcoded per-mode action.

api_frames.py, manage.py, and common.py's build_manage_content are
repointed to read/write the frame's widget config rows instead of
the old Frame columns, and every settings page (Photos/Calendar/
Whiteboard tabs) now pre-fills its form from the same widget config
the write endpoints actually save to -- previously the read and
write sides would have silently diverged. The old mode selector and
photo-inlay checkbox are removed along with their now-inert wiring;
arbitrary widget placement subsumes what the fixed inlay split did.

Ships together with Phase 1 (per-type render/action modules) since
splitting the read/write cutover across deploys would have left
settings changes with no visible effect.

server/app/widgets/calendar.py

@@ -34,7 +34,19 @@ from ..routers.common import (
 ACTION_LABELS = {"advance": "Next period", "back": "Previous period"}
 
 
-def render(db: Session, frame: Frame, widget: Widget, target_w: int, target_h: int) -> Image.Image:
+def render(db: Session, frame: Frame, widget: Widget, target_w: int, target_h: int,
+          is_normal_wake: bool = True) -> Image.Image:
+    """is_normal_wake=True (an ordinary /frame/image GET, not a button
+    press) resets browse_offset back to "today" if it had drifted --
+    mirrors the old _render_calendar_mode's identical behavior. A button
+    press explicitly moved the browse position on purpose, so it passes
+    is_normal_wake=False to render its own already-updated offset instead
+    of immediately snapping back to 0."""
+    if is_normal_wake:
+        with widget_locked(db, frame.id, widget.id) as (_, _, locked_cfg):
+            if locked_cfg.browse_offset != 0:
+                locked_cfg.browse_offset = 0
+
     cfg = db.get(CalendarWidgetConfig, widget.id)
     events, fetch_summary = get_or_refresh_calendar_events_for_widget(db, frame, widget)
     weather_cities = get_or_refresh_weather_for_widget(db, frame, widget) if cfg.weather_enabled else None