2c9ca0d6b4
- Remove server-side broadcast_loop (MPV position polling eliminated)
- Browser sends {type: tick, position: N} at ~10Hz
- Server looks up nearest beat within 50ms window, sends {type: beat, position, tempo}
- Browser sends play/pause/seek events (logged, no UDP yet)
- Browser sends {type: load, path} to switch beat cache to specific file
- _find_nearest_beat() uses bisect for O(log n) lookup
- Per-connection beat state: current_file, beats list, tempo, last_beat_reported