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/whiteboard.py

@@ -22,7 +22,11 @@ from ._shared import placeholder_image
 ACTION_LABELS = {"check_now": "Check for updates"}
 
 
-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 is unused here -- see app/widgets/photos.py's
+    identical note; every widget type's render() shares one call
+    signature regardless of which ones actually care."""
     png_bytes = get_or_refresh_whiteboard_for_widget(db, frame, widget)
     if png_bytes is None:
         return placeholder_image(target_w, target_h, ["Whiteboard widget", "not configured yet"])