Scheduler Event Timeline Navigation

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

Navigation steps follow the active TimelinePreset — day presets shift by hours, week presets by days.

• Wiring external "today" or paging buttons outside the timeline toolbar
• Syncing visible_date with URL query params or parent view state

• Bind visible_date: RwSignal<OrbitalDateTime> on SchedulerTimeline.
• Bind preset: RwSignal<TimelinePreset> so prev/next step sizes match zoom level.
• Capture SchedulerTimelineHandle via on_handle for imperative go_to_today, go_to_previous, and go_to_next.