Six tables: channels, playlists, items, sidecars (sidecar registry for
health-check), schedule (Phase B), as-run log.
- video_format default 1080p5994 (house standard, capture cadence)
- restart_count / last_restart_at / last_heartbeat_at on channels for
auto-failover bookkeeping
- audio_normalized flag on items so re-stages skip the loudnorm pass
- unique partial index on (channel_id) for running sidecars
