Dashboard widget: a compact month grid with a dot on each day the viewer has an event, today highlighted.
Rendered by phoenix_kit_dashboards (duck-typed contract — see
PhoenixKitCalendar.phoenix_kit_widgets/0). The grid itself is
PhoenixLiveCalendar.Components.MiniCalendar; we only feed it the viewer's
own events grouped by their LOCAL date (their offset frame), so day markers
don't drift around UTC midnight and a shared dashboard never leaks anyone
else's events. Renders defensively — any failure degrades to an empty month.