Move mode picker below device status bar; fix invisible calendar lines; add CalDAV calendar support

Calendar rule/grid lines were light gray, which dithers away to
near-invisible on the 6-color e-ink palette -- now black.

CalDAV accounts (Nextcloud, Fastmail, iCloud, ...) can now be linked
alongside the existing single ICS subscription, since one account can
expose several calendars. A frame's Calendar tab now lists calendars
per person rather than one opt-in per person: your own row shows every
calendar you have available with a full add/remove toggle, while other
linked users' rows show only calendars they've included, toggleable
off (mute) but not on -- only a calendar's owner can add it to a
shared frame. FrameCalendar replaces the old single-boolean
UserFrame.calendar_included; existing opt-ins are migrated forward.

server/app/routers/api_frames.py

@@ -36,7 +36,7 @@ from ..image_pipeline import (
     render_preview_png,
 )
 from ..firmware import firmware_path, parse_app_version
-from ..models import BatteryLog, Frame, UserFrame
+from ..models import BatteryLog, Frame, FrameCalendar
 from .common import (
     FRAME_MODES,
     OVERDUE_FACTOR,
@@ -409,33 +409,53 @@ def api_preview_rendered(frame: Frame = Depends(require_frame_view), db: Session
     return Response(content=png, media_type="image/png")
 
 
-class CalendarIncludedRequest(BaseModel):
+class CalendarSelectRequest(BaseModel):
+    user_id: int
+    calendar_key: str
+    calendar_label: str = ""
     included: bool
 
 
-@router.post("/api/frames/{frame_id}/calendar-included")
-def api_calendar_included(
-    body: CalendarIncludedRequest,
+@router.post("/api/frames/{frame_id}/calendar-select")
+def api_calendar_select(
+    body: CalendarSelectRequest,
     request: Request,
     frame: Frame = Depends(require_frame_view),  # view access only -- NOT require_frame_control
     db: Session = Depends(get_db),
 ):
-    """A user's own opt-in into this frame's merged calendar (see
-    UserFrame.calendar_included). Deliberately not require_frame_control:
-    this is the toggling user's own data-sharing preference about their
-    own calendar, not a frame setting its controller manages on someone
-    else's behalf -- there's no target user_id in the request body by
-    design, it always toggles the calling session's own row."""
+    """Include/exclude one calendar (calendar_key "ics" or
+    "caldav:<href>", see FrameCalendar) on this frame. Deliberately not
+    require_frame_control: adding your own calendar, or muting anyone's
+    (including your own), is each viewer's own call, not something a
+    frame's controller manages on someone else's behalf. The one-sided
+    permission split lives here: turning a calendar ON requires being its
+    owner (nobody can add someone else's calendar to a shared frame for
+    them); turning one OFF only requires being linked to the frame at
+    all, so anyone sharing the display can mute a calendar they'd rather
+    not see there even if they don't own it."""
     user = require_user_api(request, db)
-    row = db.get(UserFrame, (user.id, frame.id))
+    if body.included and body.user_id != user.id:
+        raise HTTPException(403, "Only a calendar's owner can add it to a frame")
+    row = db.execute(
+        select(FrameCalendar).where(
+            FrameCalendar.frame_id == frame.id,
+            FrameCalendar.user_id == body.user_id,
+            FrameCalendar.calendar_key == body.calendar_key,
+        )
+    ).scalar_one_or_none()
     if row is None:
-        raise HTTPException(404, "Not linked to this frame")
-    row.calendar_included = body.included
+        if not body.included:
+            raise HTTPException(404, "Not currently included on this frame")
+        row = FrameCalendar(frame_id=frame.id, user_id=body.user_id, calendar_key=body.calendar_key)
+        db.add(row)
+    row.included = body.included
+    if body.calendar_label:
+        row.calendar_label = body.calendar_label
     # Force this frame's merged cache to pick up the change promptly
     # rather than waiting out the throttle.
     frame.calendar_checked_at = 0.0
     db.commit()
-    return {"status": "saved", "included": row.calendar_included}
+    return {"status": "saved", "included": row.included}
 
 
 def _calendar_photo_inlay(frame: Frame, db: Session):