Scheduler Calendar Navigation

Move the visible calendar range with toolbar controls or an imperative handle.

• Wiring external paging or "today" buttons outside the calendar toolbar
• Syncing visible_date with routing or parent tabs

• Bind visible_date: RwSignal<OrbitalDateTime> and view: RwSignal<SchedulerView>.
• Capture SchedulerCalendarHandle via scheduler_events.on_calendar_handle for go_to_today, go_to_previous, and go_to_next.
• Display the formatted range label from visible_date + view in your own chrome if needed.