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/models.py

@@ -202,6 +202,33 @@ class Frame(Base):
     calendar_weather_checked_at: Mapped[float] = mapped_column(Float, default=0.0)
     calendar_weather_cached: Mapped[list | None] = mapped_column(JSON, nullable=True, default=None)
 
+    # Week view: how many days to show (2-10, default 7 -- the original
+    # fixed behavior) and whether they're laid out as side-by-side
+    # columns or stacked bands (see calendar_render.py's _build_week).
+    calendar_week_days: Mapped[int] = mapped_column(Integer, default=7)
+    calendar_week_layout: Mapped[str] = mapped_column(String, default="horizontal")  # "horizontal" | "vertical"
+
+    # Optional task list, week view only -- takes the space of one day
+    # slot rather than adding an extra one (see calendar_render.py's
+    # _draw_tasks). CalDAV only (a task list is a VTODO collection, not
+    # something a plain ICS subscription meaningfully has); source is
+    # one specific linked user's own CalDAV calendar, same
+    # owner-controls-their-own-data permission split as FrameCalendar --
+    # see routers/api_frames.py's api_tasks_source. calendar_tasks_user_id
+    # SET NULL on the user's deletion clears the source rather than
+    # leaving a dangling reference (checked_at isn't reset by that, but
+    # the next refresh attempt finds no source and just returns []).
+    calendar_tasks_enabled: Mapped[bool] = mapped_column(Boolean, default=False)
+    calendar_tasks_user_id: Mapped[int | None] = mapped_column(
+        ForeignKey("users.id", ondelete="SET NULL"), nullable=True
+    )
+    calendar_tasks_calendar_key: Mapped[str | None] = mapped_column(String, nullable=True)
+    calendar_tasks_checked_at: Mapped[float] = mapped_column(Float, default=0.0)
+    # [{"summary", "due" (ISO date/datetime string or None)}, ...],
+    # already filtered to outstanding (not-completed) tasks and sorted
+    # by due date -- see caldav_client.fetch_tasks.
+    calendar_tasks_cached: Mapped[list | None] = mapped_column(JSON, nullable=True, default=None)
+
     # -- state --
     current_asset_id: Mapped[str] = mapped_column(String, default="")
     current_asset_set_at: Mapped[float] = mapped_column(Float, default=0.0)