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/app/calendar_render.py

@@ -530,8 +530,12 @@ def _draw_agenda_day(img: Image.Image, draw: ImageDraw.ImageDraw, day: date, eve
 
 def _draw_tasks(img: Image.Image, draw: ImageDraw.ImageDraw, region: tuple[int, int, int, int],
                 tasks: list[dict], title_font: ImageFont.ImageFont, body_font: ImageFont.ImageFont,
-                palette_rgb: list | None = None) -> None:
-    """A simple checklist filling `region` (x0, y0, w, h) -- a color bar
+                palette_rgb: list | None = None, title: str = "Tasks") -> None:
+    """A simple checklist filling `region` (x0, y0, w, h) -- a header
+    (`title`, truncated to fit -- TaskWidgetConfig.name or the "Tasks"
+    default; the only widget type with its own on-panel title, since
+    it's the only one where "which list is this" isn't obvious from its
+    content the way a calendar/photo/whiteboard's is), then a color bar
     (reusing _event_colors/_draw_color_bar as-is: a task dict's
     top-level owner_display_name/color_index is exactly _event_colors'
     single-source fallback shape, since caldav_client.merge_tasks
@@ -551,7 +555,7 @@ def _draw_tasks(img: Image.Image, draw: ImageDraw.ImageDraw, region: tuple[int,
     x0, y0, w, h = region
     text_x0, text_y0 = x0 + MARGIN, y0 + MARGIN
     text_w = w - MARGIN * 2
-    draw_text(img, (text_x0, text_y0), "Tasks", title_font)
+    draw_text(img, (text_x0, text_y0), _truncate_to_width(draw, title or "Tasks", title_font, text_w), title_font)
     y = text_y0 + title_font.size + 12
     draw.line([(text_x0, y), (text_x0 + text_w, y)], fill=RULE)
     y += 12
@@ -894,7 +898,8 @@ def render_calendar_preview_png(events: list[dict], view: str, browse_offset: in
 _TASKS_FONTS = {"large": (24, 18), "medium": (20, 16), "small": (16, 13)}
 
 
-def _build_tasks(tasks: list[dict], target_w: int, target_h: int, palette_rgb: list | None = None) -> Image.Image:
+def _build_tasks(tasks: list[dict], target_w: int, target_h: int, palette_rgb: list | None = None,
+                 title: str = "Tasks") -> Image.Image:
     """A tasks widget's entire region is the checklist -- unlike the old
     week-view slot, there's no day columns/header to share space with,
     so this is just _draw_tasks over the whole box."""
@@ -903,29 +908,29 @@ def _build_tasks(tasks: list[dict], target_w: int, target_h: int, palette_rgb: l
     title_size, body_size = _TASKS_FONTS[_size_tier(target_w, target_h)]
     title_font = ImageFont.load_default(size=title_size)
     body_font = ImageFont.load_default(size=body_size)
-    _draw_tasks(img, draw, (0, 0, target_w, target_h), tasks, title_font, body_font, palette_rgb)
+    _draw_tasks(img, draw, (0, 0, target_w, target_h), tasks, title_font, body_font, palette_rgb, title)
     return img
 
 
 def render_tasks(tasks: list[dict], orientation: str, palette_rgb: list | None,
-                 manage: dict | None = None) -> bytes:
+                 manage: dict | None = None, title: str = "Tasks") -> bytes:
     """Renders the tasks widget full-panel to the panel's packed format.
     Always returns exactly EPD_WIDTH*EPD_HEIGHT/2 bytes, same invariant
     every other renderer honors."""
     target_w, target_h = logical_render_size(orientation)
-    img = _build_tasks(tasks, target_w, target_h, palette_rgb)
+    img = _build_tasks(tasks, target_w, target_h, palette_rgb, title)
     img = _apply_manage_overlay(img, manage)
     quantized = _quantize(img, palette_rgb, dither_strength=1.0)
     return _transpose_and_pack(quantized, orientation)
 
 
 def render_tasks_preview_png(tasks: list[dict], orientation: str, palette_rgb: list | None,
-                             manage: dict | None = None) -> bytes:
+                             manage: dict | None = None, title: str = "Tasks") -> bytes:
     """Same pipeline as render_tasks, but a normal browser-viewable PNG
     in logical (upright) orientation -- mirrors render_calendar_preview_
     png's relationship to render_calendar."""
     target_w, target_h = logical_render_size(orientation)
-    img = _build_tasks(tasks, target_w, target_h, palette_rgb)
+    img = _build_tasks(tasks, target_w, target_h, palette_rgb, title)
     img = _apply_manage_overlay(img, manage)
     quantized = _quantize(img, palette_rgb, dither_strength=1.0)
     buf = io.BytesIO()