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/migration.py

@@ -160,6 +160,18 @@ def _migration_10(conn) -> None:
     conn.execute(text("ALTER TABLE frames ADD COLUMN calendar_weather_cached TEXT"))
 
 
+def _migration_11(conn) -> None:
+    """Manual per-calendar color choice (frame_calendars.color_index,
+    2-5 into image_pipeline.DEFAULT_PALETTE_RGB -- Yellow/Red/Blue/
+    Green). calendar_render.py's event color bar/dot used to auto-cycle
+    through those same four colors in whatever order calendars happened
+    to appear; this lets a household pin a specific one instead so it
+    stays stable and recognizable. NULL (the default) keeps the old
+    auto-cycle behavior -- no existing frame's render changes until
+    someone actually picks a color."""
+    conn.execute(text("ALTER TABLE frame_calendars ADD COLUMN color_index INTEGER"))
+
+
 MIGRATIONS = [
     (1, _migration_1),
     (2, _migration_2),
@@ -171,6 +183,7 @@ MIGRATIONS = [
     (8, _migration_8),
     (9, _migration_9),
     (10, _migration_10),
+    (11, _migration_11),
 ]