Week view flexibility: configurable day count, layout, and a CalDAV task list

- Day count (2-10, was fixed at 7) -- 5 days trims the weekend clutter
  without losing the grid format.
- Layout choice: days side by side (original behavior) or stacked
  vertically as full agenda-style sections (reuses _draw_agenda_day,
  same approach _build_today_tomorrow already used for a fixed 2 days).
- Optional task list (CalDAV VTODO collections only -- a plain ICS
  subscription doesn't meaningfully have one) that takes the space of
  one day slot instead of adding an extra one. Same owner-controls-
  their-own-data permission split as calendar sources: only the
  calendar's owner can point a frame's task list at it, but anyone
  linked to the frame can clear it.

Browse-offset paging now moves by N days (was hardcoded to weeks),
identical to the old behavior when days=7. Changing the day count
resets the browse offset, same reasoning as changing views already did.

server/app/migration.py

@@ -172,6 +172,23 @@ def _migration_11(conn) -> None:
     conn.execute(text("ALTER TABLE frame_calendars ADD COLUMN color_index INTEGER"))
 
 
+def _migration_12(conn) -> None:
+    """Week view flexibility: a configurable day count (2-10, default 7
+    -- the original fixed behavior) and a horizontal/vertical layout
+    choice, plus an optional CalDAV task list that takes the space of
+    one day slot when enabled (see calendar_render.py's _build_week/
+    _draw_tasks). Every new column has a behavior-preserving default --
+    no existing frame's render changes until its Calendar tab touches
+    one of these."""
+    conn.execute(text("ALTER TABLE frames ADD COLUMN calendar_week_days INTEGER NOT NULL DEFAULT 7"))
+    conn.execute(text("ALTER TABLE frames ADD COLUMN calendar_week_layout TEXT NOT NULL DEFAULT 'horizontal'"))
+    conn.execute(text("ALTER TABLE frames ADD COLUMN calendar_tasks_enabled INTEGER NOT NULL DEFAULT 0"))
+    conn.execute(text("ALTER TABLE frames ADD COLUMN calendar_tasks_user_id INTEGER REFERENCES users(id) ON DELETE SET NULL"))
+    conn.execute(text("ALTER TABLE frames ADD COLUMN calendar_tasks_calendar_key TEXT"))
+    conn.execute(text("ALTER TABLE frames ADD COLUMN calendar_tasks_checked_at REAL NOT NULL DEFAULT 0.0"))
+    conn.execute(text("ALTER TABLE frames ADD COLUMN calendar_tasks_cached TEXT"))
+
+
 MIGRATIONS = [
     (1, _migration_1),
     (2, _migration_2),
@@ -184,6 +201,7 @@ MIGRATIONS = [
     (9, _migration_9),
     (10, _migration_10),
     (11, _migration_11),
+    (12, _migration_12),
 ]