Session recording and playback for debrief

Let instructors record a session as it happens and play it back afterward for debrief — watching the monitor replay exactly what occurred (vitals, waveforms, rhythm changes, shocks, pacing) instead of just reading a text log of events.

Playback should run at the same real-time speed as the original session by default, since timing is often part of the lesson (e.g. how long it took to shock or start compressions). It should also support fast-forwarding through quiet stretches, jumping straight to a specific event, and pausing to discuss a moment.

This is different from our Event Log (a written summary) and from Scenarios (a preset starting point loaded before a session begins) — this captures what actually happened during a specific live run.