Split the tasks feature out of the calendar widget into its own widget type

Task lists used to be a week-view-only sub-feature bolted onto calendar
widgets (CalendarWidgetConfig.tasks_*), so a task list could only exist
tied to a calendar's view and only inside its footprint. Tasks are now
a standalone widget type (TaskWidgetConfig, app/widgets/tasks.py) that
can be placed and sized independently, same as photos/calendar/
whiteboard -- no separate "enabled" flag either, since being on the
grid at all is the on/off switch, matching every other widget type.

Migration 17 creates task_widget_configs, extracts any existing
calendar widget's configured task source into a new sibling tasks
widget (auto-placed in open grid space, source dropped+logged if truly
none is left), then drops calendar_widget_configs' now-dead tasks_*
columns in the same migration -- this project's usual same-migration-
drop convention. Also handles the rarer case of a database jumping
straight from before the widget system existed to after this split in
one boot, via the legacy Frame.calendar_tasks_* columns.

Verified live in the browser at desktop and mobile widths: adding a
Tasks widget, its own dialog (task-list source picker + preview), and
confirming the calendar widget's dialog no longer mentions tasks at
all. Full test suite (180 tests, including new coverage for the widget
render/actions, the migration's data-extraction path, and the
permission-boundary shape for tasks-source) passes.

server/app/routers/api_widgets.py

@@ -1,8 +1,8 @@
 """Everything scoped to one specific widget rather than "the frame":
 placement CRUD (backing the Layout tab's canvas, static/frame_layout.js)
 plus every setting/action that used to assume a frame had at most one
-widget of a given type -- photo queue, calendar inclusion/color/tasks,
-whiteboard source, and their preview endpoints. Split out of
+widget of a given type -- photo queue, calendar inclusion/color, tasks
+source, whiteboard source, and their preview endpoints. Split out of
 api_frames.py (which keeps frame-wide settings: orientation, quiet
 hours, palette, firmware, stats) once a frame could hold more than one
 widget of the same type, at which point "the frame's calendar settings"
@@ -35,6 +35,7 @@ from ..models import (
     Frame,
     FrameCalendar,
     PhotoWidgetConfig,
+    TaskWidgetConfig,
     WhiteboardWidgetConfig,
     WIDGET_CONFIG_MODELS,
     Widget,
@@ -254,7 +255,6 @@ def api_widget_config_save(
     calendar_week_start_offset: int | None = Form(None),
     calendar_weather_enabled: bool | None = Form(None),
     calendar_weather_units: str | None = Form(None),
-    calendar_tasks_enabled: bool | None = Form(None),
 ):
     """Every field optional -- same partial-update, form-urlencoded
     convention as the old frame-level api_config_save, now scoped to one
@@ -317,8 +317,6 @@ def api_widget_config_save(
                     # new unit label.
                     ccfg.weather_checked_at = 0.0
                 ccfg.weather_units = calendar_weather_units
-            if calendar_tasks_enabled is not None:
-                ccfg.tasks_enabled = calendar_tasks_enabled
     with frame_locked(db, frame.id) as cfg:
         cfg.stats_config_saves += 1
     return {"status": "saved"}
@@ -506,7 +504,7 @@ def api_widget_preview_rendered(
     return Response(content=png, media_type="image/png")
 
 
-# --- Calendar: inclusion/color/tasks/weather/preview --------------------
+# --- Calendar: inclusion/color/weather/preview ---------------------------
 
 class CalendarSelectRequest(BaseModel):
     user_id: int
@@ -609,21 +607,37 @@ def api_widget_preview_calendar(
     ccfg = db.get(CalendarWidgetConfig, widget.id)
     events, summary = get_or_refresh_calendar_events_for_widget(db, frame, widget)
     weather_cities = get_or_refresh_weather_for_widget(db, frame, widget) if ccfg.weather_enabled else None
-    tasks = (
-        get_or_refresh_tasks_for_widget(db, frame, widget)
-        if (ccfg.view == "week" and ccfg.tasks_enabled) else None
-    )
     png = calendar_render.render_calendar_preview_png(
         events, view=ccfg.view, browse_offset=ccfg.browse_offset, orientation=frame.orientation,
         palette_rgb=frame.palette_rgb, timezone=frame.timezone, fetch_summary=summary,
         week_start=ccfg.week_start,
         weather_cities=weather_cities, weather_units=ccfg.weather_units,
-        week_days=ccfg.week_days, week_layout=ccfg.week_layout, tasks=tasks,
+        week_days=ccfg.week_days, week_layout=ccfg.week_layout,
         week_start_offset=ccfg.week_start_offset,
     )
     return Response(content=png, media_type="image/png")
 
 
+# --- Tasks: source/preview ------------------------------------------------
+
+@router.get("/api/frames/{frame_id}/widgets/{widget_id}/preview/tasks")
+def api_widget_preview_tasks(
+    frame_widget: tuple[Frame, Widget] = Depends(require_widget_view), db: Session = Depends(get_db)
+):
+    """The same cached task list a live device render would use, same
+    "reflects what's currently saved" convention as the other preview
+    endpoints."""
+    frame, widget = frame_widget
+    _require_widget_type(widget, "tasks")
+    tcfg = db.get(TaskWidgetConfig, widget.id)
+    if not tcfg.calendar_key or not tcfg.user_id:
+        raise HTTPException(400, "No task list configured on this widget yet")
+    tasks = get_or_refresh_tasks_for_widget(db, frame, widget)
+    png = calendar_render.render_tasks_preview_png(tasks, orientation=frame.orientation,
+                                                    palette_rgb=frame.palette_rgb)
+    return Response(content=png, media_type="image/png")
+
+
 class TasksSourceRequest(BaseModel):
     calendar_key: str | None  # None clears the source
 
@@ -634,27 +648,27 @@ def api_widget_tasks_source(
     frame_widget: tuple[Frame, Widget] = Depends(require_widget_view),
     db: Session = Depends(get_db),
 ):
-    """Points this widget's week-view task list at one of the calling
-    user's own CalDAV calendars -- same owner-controls-their-own-data
-    permission split as calendar-select's included=True, since this is
-    volunteering personal calendar data, not a display setting a
-    controller should get to pick on someone else's behalf. None clears
-    the source; clearing (unlike setting) isn't ownership-gated -- like
-    muting a shared calendar, anyone linked to the frame can turn off a
-    task list they'd rather not see, but only its owner can point the
-    widget at one of their calendars to begin with."""
+    """Points this tasks widget at one of the calling user's own CalDAV
+    calendars -- same owner-controls-their-own-data permission split as
+    calendar-select's included=True, since this is volunteering personal
+    calendar data, not a display setting a controller should get to pick
+    on someone else's behalf. None clears the source; clearing (unlike
+    setting) isn't ownership-gated -- like muting a shared calendar,
+    anyone linked to the frame can turn off a task list they'd rather
+    not see, but only its owner can point the widget at one of their
+    calendars to begin with."""
     frame, widget = frame_widget
-    _require_widget_type(widget, "calendar")
+    _require_widget_type(widget, "tasks")
     user = require_user_api(request, db)
     with widget_locked(db, frame.id, widget.id) as (_, _, cfg):
         if body.calendar_key is None:
-            cfg.tasks_user_id = None
-            cfg.tasks_calendar_key = None
-            cfg.tasks_cached = None
+            cfg.user_id = None
+            cfg.calendar_key = None
+            cfg.cached = None
         else:
-            cfg.tasks_user_id = user.id
-            cfg.tasks_calendar_key = body.calendar_key
-        cfg.tasks_checked_at = 0.0  # pick up the change promptly
+            cfg.user_id = user.id
+            cfg.calendar_key = body.calendar_key
+        cfg.checked_at = 0.0  # pick up the change promptly
     return {"status": "saved", "calendar_key": body.calendar_key}