Let a tasks widget merge multiple task lists, checkbox+color like calendar

Tasks widgets could only ever point at one CalDAV task list (a radio-
button picker, owner-only). Now they merge any number of included task
lists across every linked user, same checkbox-inclusion + optional
pinned-color shape a calendar widget already has for its calendars --
FrameTaskList mirrors FrameCalendar exactly, down to the same owner-
adds/anyone-mutes permission split (api_widget_task_list_select/
api_widget_task_list_color). Reused calendar_render._event_colors/
_draw_color_bar as-is for the per-task color bar -- a task dict's
owner_display_name/color_index is exactly that function's single-
source fallback shape.

Also added an opt-in "show tasks completed in the last 24 hours"
toggle (TaskWidgetConfig.show_completed): caldav_client.fetch_tasks
now accepts a completed_since cutoff and returns completed VTODOs
(with their completion time) instead of silently dropping them, and
_draw_tasks gives a completed task a filled checkbox + muted text
instead of the normal empty-box/due-date row.

Migration 18 splits the single-source TaskWidgetConfig columns
(added by 17, splitting tasks out of the calendar widget in the first
place) into frame_task_lists, carrying forward each widget's existing
single source as its first included list -- same shape migration 9
used carrying forward frame_calendars' old single opt-in.

Verified live in the browser (desktop + mobile): the new "Included
task lists" + "Recently completed" dialog sections, the show_completed
toggle actually persisting through a real HTTP round-trip, and no
regression in the calendar widget's own "Included calendars" dialog.
Full suite (192 tests, including new merge_tasks/config_save/migration
coverage) passes.

server/tests/test_widgets_tasks.py

@@ -1,8 +1,11 @@
 """app.widgets.tasks -- unit-level, no HTTP: constructs Widget/
 TaskWidgetConfig rows directly and monkeypatches the underlying fetch
-call (get_or_refresh_tasks_for_widget, throttle/CalDAV-fetch logic
-covered separately). Split out of the old calendar widget's week-view-
-only task list -- see models.TaskWidgetConfig."""
+call (get_or_refresh_tasks_for_widget, throttle/multi-list-merge/CalDAV
+-fetch logic covered separately -- see test_widget_config_and_queue_
+endpoints.py and test_permission_boundaries.py for the FrameTaskList
+inclusion/color HTTP-layer coverage). Split out of the old calendar
+widget's week-view-only, single-list task list -- see
+models.TaskWidgetConfig/FrameTaskList."""
 
 from __future__ import annotations
 
@@ -11,8 +14,6 @@ import time
 from app import widgets
 from app.models import Frame, TaskWidgetConfig, Widget
 
-from .conftest import make_user
-
 
 def _make_widget(db_session, **cfg_kwargs) -> tuple[Frame, Widget]:
     frame = db_session.get(Frame, 1)
@@ -25,30 +26,44 @@ def _make_widget(db_session, **cfg_kwargs) -> tuple[Frame, Widget]:
     return frame, widget
 
 
-def _make_configured_widget(db_session) -> tuple[Frame, Widget]:
-    user = make_user(db_session, "task-owner")
-    return _make_widget(db_session, user_id=user.id, calendar_key="caldav:/some/tasks/")
-
-
-def test_render_unconfigured_widget_returns_correctly_sized_placeholder(db_session):
-    frame, widget = _make_widget(db_session)  # no user_id/calendar_key set
-    img = widgets.tasks.render(db_session, frame, widget, 300, 200)
-    assert img.size == (300, 200)
-
-
-def test_render_configured_widget_produces_a_correctly_sized_image(db_session, monkeypatch):
-    frame, widget = _make_configured_widget(db_session)
-    monkeypatch.setattr(widgets.tasks, "get_or_refresh_tasks_for_widget",
-                        lambda db, frame, widget: [{"summary": "Buy milk", "due": None}])
+def test_render_produces_a_correctly_sized_image_with_no_lists_included(db_session, monkeypatch):
+    """No placeholder for "nothing included yet" -- same posture as
+    app/widgets/calendar.py (see tasks.py's own module docstring):
+    get_or_refresh_tasks_for_widget already returns [] with nothing
+    included, and render() draws straight through that."""
+    frame, widget = _make_widget(db_session)
+    monkeypatch.setattr(widgets.tasks, "get_or_refresh_tasks_for_widget", lambda db, frame, widget: [])
 
     img = widgets.tasks.render(db_session, frame, widget, 300, 200)
     assert img.size == (300, 200)
     assert img.mode == "RGB"
 
 
-def test_render_configured_but_empty_task_list_still_renders(db_session, monkeypatch):
-    frame, widget = _make_configured_widget(db_session)
-    monkeypatch.setattr(widgets.tasks, "get_or_refresh_tasks_for_widget", lambda db, frame, widget: [])
+def test_render_produces_a_correctly_sized_image_with_tasks(db_session, monkeypatch):
+    frame, widget = _make_widget(db_session)
+    monkeypatch.setattr(widgets.tasks, "get_or_refresh_tasks_for_widget",
+                        lambda db, frame, widget: [
+                            {"summary": "Buy milk", "due": None, "completed_at": None,
+                             "owner_display_name": "Alice", "color_index": None},
+                        ])
+
+    img = widgets.tasks.render(db_session, frame, widget, 300, 200)
+    assert img.size == (300, 200)
+    assert img.mode == "RGB"
+
+
+def test_render_with_completed_tasks(db_session, monkeypatch):
+    """show_completed's merged result includes completed tasks too (see
+    caldav_client.fetch_tasks' completed_since) -- render() must handle
+    that shape (a non-None completed_at) without error."""
+    frame, widget = _make_widget(db_session)
+    monkeypatch.setattr(widgets.tasks, "get_or_refresh_tasks_for_widget",
+                        lambda db, frame, widget: [
+                            {"summary": "Walk the dog", "due": "2026-08-01", "completed_at": None,
+                             "owner_display_name": "Alice", "color_index": 2},
+                            {"summary": "Buy milk", "due": None, "completed_at": "2026-08-01T10:00:00+00:00",
+                             "owner_display_name": "Alice", "color_index": 2},
+                        ])
 
     img = widgets.tasks.render(db_session, frame, widget, 300, 200)
     assert img.size == (300, 200)
@@ -58,7 +73,7 @@ def test_render_at_minimum_grid_footprint(db_session, monkeypatch):
     """grid.MIN_FOOTPRINT["tasks"] is (2, 2) cells -- on an 8x5 grid
     against a full 800x480 panel that's a 200x192 box, the smallest a
     tasks widget can actually be placed at."""
-    frame, widget = _make_configured_widget(db_session)
+    frame, widget = _make_widget(db_session)
     monkeypatch.setattr(widgets.tasks, "get_or_refresh_tasks_for_widget", lambda db, frame, widget: [])
 
     img = widgets.tasks.render(db_session, frame, widget, 200, 192)