Add a per-widget text-size picker for calendar/tasks legibility

Calendar and tasks pack the most body text at the smallest default
sizes, so those two gear-icon dialogs get a "Text size" card (Normal/
Large/X-Large) alongside the existing Border card -- a new Widget-level
font_scale column with its own POST .../font-scale endpoint, same
Widget-property-not-config-field shape as border_style. Threaded through
every classic (calendar_render.py) and modern (html_render.py/
calendar_html_render.py) size calc via one shared panel_style.
scaled_size() so row heights/max_rows already derived from font size
re-fit around the bigger text automatically.

server/app/models.py

@@ -499,6 +499,12 @@ class Widget(Base):
     border_style: Mapped[str] = mapped_column(String, default="none")
     border_thickness: Mapped[int] = mapped_column(Integer, default=3)
     border_color_index: Mapped[int] = mapped_column(Integer, default=0)
+    # Text-size multiplier for this widget's own body/title text -- another
+    # Widget-level property regardless of widget_type, same reasoning as
+    # border_style above (any widget type with text can use it). One of
+    # panel_style.FONT_SCALE_CHOICES; 1.0 (unchanged size) for every
+    # existing widget until its dialog's "Text size" picker sets it.
+    font_scale: Mapped[float] = mapped_column(Float, default=1.0)
 
     __table_args__ = (Index("ix_widgets_frame", "frame_id"),)