- Add `check_room_access` before `manager.subscribe()` in ws_universal
to prevent unauthorized room subscription (security fix)
- Fix busy-wait in `poll_push_streams`: sleep 50ms when streams are
empty, yield only when there are active streams
- Re-subscribe dead rooms after stream errors so events are not
permanently lost until manual reconnect
- Fix streaming message placeholder using fake content as room_id:
use chunk.room_id from backend instead
- Show toast error on history load failures instead of silent fallback
