Add camera_event_subscriptions table to track per-camera per-topic
subscription state (inactive/pending/active/failed). Refresh-events
handler now merges discovered topics instead of replacing, so topics
are never lost when a camera goes temporarily offline. Admin UI shows
colored status dots and last-event timestamps per topic, with a
"subscribe all inactive" button to queue subscriptions for kiosk pickup.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>