Let a tasks widget have a custom on-panel name

Adds TaskWidgetConfig.name (migration 19, plain column add) shown at
the top of the widget on the actual panel instead of the hardcoded
"Tasks" header -- e.g. "Chores" or "Mom's list". The only widget type
with its own on-panel title at all, since it's the only one where
"which list is this" isn't already obvious from a calendar/photo/
whiteboard's own content.

Threaded through calendar_render's _draw_tasks/_build_tasks/
render_tasks/render_tasks_preview_png as a `title` param (default
"Tasks", truncated to fit -- a long custom name shouldn't be able to
overflow the widget's box), the config-save endpoint (tasks_name,
truncated server-side to a sane header length rather than rejected),
and a new "Settings" section in the tasks dialog.

Verified live in the browser: the name actually renders at the top of
the real composited panel (not just the dialog preview, which stays
gated on having a configured source), and persists correctly on both
desktop and mobile. Full suite (196 tests) passes.

server/tests/test_widgets_tasks.py

@@ -69,6 +69,50 @@ def test_render_with_completed_tasks(db_session, monkeypatch):
     assert img.size == (300, 200)
 
 
+def _capture_build_tasks_title(monkeypatch):
+    """Wraps the real _build_tasks to record the `title` it was called
+    with, while still rendering for real (not a bare stub) so this
+    keeps exercising the actual render path."""
+    seen_titles = []
+    real_build_tasks = widgets.tasks._build_tasks
+
+    def spy(tasks, target_w, target_h, palette_rgb=None, title="Tasks"):
+        seen_titles.append(title)
+        return real_build_tasks(tasks, target_w, target_h, palette_rgb, title)
+
+    monkeypatch.setattr(widgets.tasks, "_build_tasks", spy)
+    return seen_titles
+
+
+def test_render_passes_custom_name_as_title(db_session, monkeypatch):
+    frame, widget = _make_widget(db_session, name="Chores")
+    monkeypatch.setattr(widgets.tasks, "get_or_refresh_tasks_for_widget", lambda db, frame, widget: [])
+    seen_titles = _capture_build_tasks_title(monkeypatch)
+
+    widgets.tasks.render(db_session, frame, widget, 300, 200)
+    assert seen_titles == ["Chores"]
+
+
+def test_render_falls_back_to_default_title_when_name_is_blank(db_session, monkeypatch):
+    frame, widget = _make_widget(db_session)  # name defaults to ""
+    monkeypatch.setattr(widgets.tasks, "get_or_refresh_tasks_for_widget", lambda db, frame, widget: [])
+    seen_titles = _capture_build_tasks_title(monkeypatch)
+
+    widgets.tasks.render(db_session, frame, widget, 300, 200)
+    assert seen_titles == ["Tasks"]
+
+
+def test_render_with_a_very_long_custom_name_still_fits(db_session, monkeypatch):
+    """calendar_render._draw_tasks truncates the title to fit -- a name
+    far longer than any placed widget could display must not error or
+    overflow the requested size."""
+    frame, widget = _make_widget(db_session, name="A" * 200)
+    monkeypatch.setattr(widgets.tasks, "get_or_refresh_tasks_for_widget", lambda db, frame, widget: [])
+
+    img = widgets.tasks.render(db_session, frame, widget, 200, 192)
+    assert img.size == (200, 192)
+
+
 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