Dashboard widget: the viewer's schedule for today — all-day events first, then timed events in chronological order.
Rendered by phoenix_kit_dashboards (duck-typed contract — see
PhoenixKitCalendar.phoenix_kit_widgets/0). Scoped to the widget VIEWER's own
calendar, so a shared dashboard never leaks anyone else's day. "Today" is the
viewer's LOCAL today (their offset frame), so it doesn't flip around UTC
midnight. Renders defensively: any failure degrades to a friendly empty
state rather than crashing the host dashboard.