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/routers/api_widgets.py

@@ -26,7 +26,7 @@ from pydantic import BaseModel
 from sqlalchemy import func, select
 from sqlalchemy.orm import Session
 
-from .. import calendar_render, grid, photo_queue, quiet_hours, weather, weather_render, webdav_client
+from .. import calendar_render, grid, panel_style, photo_queue, quiet_hours, weather, weather_render, webdav_client
 from ..auth import require_frame_control, require_frame_view, require_user_api
 from ..db import frame_locked, get_db, widget_locked
 from ..image_pipeline import (
@@ -96,7 +96,7 @@ def _widget_dict(w: Widget, locked: bool = False) -> dict:
     return {"id": w.id, "widget_type": w.widget_type, "x": w.x, "y": w.y, "w": w.w, "h": w.h,
             "sort_order": w.sort_order, "border_style": w.border_style,
             "border_thickness": w.border_thickness, "border_color_index": w.border_color_index,
-            "locked": locked}
+            "font_scale": w.font_scale, "locked": locked}
 
 
 def require_widget_view(
@@ -280,6 +280,31 @@ def api_widget_border(
     return _widget_dict(widget)
 
 
+class WidgetFontScaleRequest(BaseModel):
+    font_scale: float
+
+
+@router.post("/api/frames/{frame_id}/widgets/{widget_id}/font-scale")
+def api_widget_font_scale(
+    body: WidgetFontScaleRequest, frame_widget: tuple[Frame, Widget] = Depends(require_widget_control),
+    db: Session = Depends(get_db),
+):
+    """Sets this widget's text-size multiplier (the Layout dialog's "Text
+    size" picker) -- a shared Widget-level property (see models.Widget.
+    font_scale), not a per-type config field, since any widget type with
+    body text can use it. Its own endpoint for the same reason
+    api_widget_border has one: api_widget_config_save's per-type dispatch
+    edits a config row via widget_locked, and font_scale lives on Widget
+    itself, not any per-type config table."""
+    frame, widget = frame_widget
+    if body.font_scale not in panel_style.FONT_SCALE_CHOICES:
+        raise HTTPException(400, f"font_scale must be one of {panel_style.FONT_SCALE_CHOICES}")
+    with frame_locked(db, frame.id):
+        widget.font_scale = body.font_scale
+        db.commit()
+    return _widget_dict(widget)
+
+
 @router.delete("/api/frames/{frame_id}/widgets/{widget_id}")
 def api_widget_delete(
     widget_id: int, frame: Frame = Depends(require_frame_control), db: Session = Depends(get_db)
@@ -876,7 +901,7 @@ def api_widget_preview_calendar(
         img = calendar_html_render.build(
             events, ccfg.view, ccfg.browse_offset, target_w, target_h, tz, ccfg.week_start, frame.palette_rgb,
             weather_cities, ccfg.weather_units, ccfg.week_days, ccfg.week_layout, ccfg.week_start_offset,
-            frame.theme,
+            frame.theme, widget.font_scale,
         )
         quantized = _quantize(img, frame.palette_rgb, dither_strength=1.0)
         png = _png_bytes(quantized)
@@ -887,7 +912,7 @@ def api_widget_preview_calendar(
             week_start=ccfg.week_start,
             weather_cities=weather_cities, weather_units=ccfg.weather_units,
             week_days=ccfg.week_days, week_layout=ccfg.week_layout,
-            week_start_offset=ccfg.week_start_offset,
+            week_start_offset=ccfg.week_start_offset, font_scale=widget.font_scale,
         )
     return Response(content=png, media_type="image/png")
 
@@ -912,12 +937,14 @@ def api_widget_preview_tasks(
         from .. import html_render
 
         target_w, target_h = logical_render_size(frame.orientation)
-        img = html_render.build_tasks(tasks, target_w, target_h, frame.palette_rgb, title, frame.theme)
+        img = html_render.build_tasks(tasks, target_w, target_h, frame.palette_rgb, title, frame.theme,
+                                      widget.font_scale)
         quantized = _quantize(img, frame.palette_rgb, dither_strength=1.0)
         png = _png_bytes(quantized)
     else:
         png = calendar_render.render_tasks_preview_png(tasks, orientation=frame.orientation,
-                                                        palette_rgb=frame.palette_rgb, title=title)
+                                                        palette_rgb=frame.palette_rgb, title=title,
+                                                        font_scale=widget.font_scale)
     return Response(content=png, media_type="image/png")