Manual per-calendar color choice for calendar mode

Each linked person can pin one of the panel's four non-black/white
colors (Yellow/Red/Blue/Green) to their own calendar instead of relying
on calendar_render.py's old auto-cycle-by-owner-name order -- owner-only,
like adding a calendar in the first place. Colors resolve against
whichever palette a frame actually renders with (including a custom
Advanced configuration override), so a pinned "Blue" stays this frame's
actual blue. Event color bars/dots are also bigger and rounded now
across agenda/week/month views, easier to tell apart at a glance.

server/app/routers/api_frames.py

@@ -469,6 +469,45 @@ def api_calendar_select(
     return {"status": "saved", "included": row.included}
 
 
+CALENDAR_COLOR_INDEX_RANGE = range(2, 6)  # Yellow/Red/Blue/Green -- see PALETTE_LABELS
+
+
+class CalendarColorRequest(BaseModel):
+    calendar_key: str
+    color_index: int | None  # None clears the pin, reverting to auto-cycle
+
+
+@router.post("/api/frames/{frame_id}/calendar-color")
+def api_calendar_color(
+    body: CalendarColorRequest,
+    request: Request,
+    frame: Frame = Depends(require_frame_view),
+    db: Session = Depends(get_db),
+):
+    """Pins a specific panel color to one of your own included calendars
+    (models.FrameCalendar.color_index) -- always owner-only, unlike
+    calendar-select's included=False, since recoloring someone else's
+    calendar isn't the same kind of "I'd rather not see this" veto as
+    muting it. None clears the pin, reverting calendar_render.py to its
+    old auto-cycle-by-owner-name behavior for this calendar."""
+    user = require_user_api(request, db)
+    if body.color_index is not None and body.color_index not in CALENDAR_COLOR_INDEX_RANGE:
+        raise HTTPException(400, "color_index must be 2-5 (the panel's non-black/white colors)")
+    row = db.execute(
+        select(FrameCalendar).where(
+            FrameCalendar.frame_id == frame.id,
+            FrameCalendar.user_id == user.id,
+            FrameCalendar.calendar_key == body.calendar_key,
+        )
+    ).scalar_one_or_none()
+    if row is None:
+        raise HTTPException(404, "Not included on this frame")
+    row.color_index = body.color_index
+    frame.calendar_checked_at = 0.0
+    db.commit()
+    return {"status": "saved", "color_index": row.color_index}
+
+
 def _calendar_photo_inlay(frame: Frame, db: Session):
     """The photo-inlay's source image (any view now, not just agenda), or
     None if inlay is off or the frame's photos-mode album isn't