- Added monotonic event ID (Last-Event-ID) for reconnection support
- Events now emit typed: 'event: camera_status' for client-side filtering
- Initial connection event sends 'event: connected' with ID
- Reconnection acknowledgment via Last-Event-ID header
- CORS preflight (OPTIONS) handler
- Access-Control-Allow-Headers: Last-Event-ID
- Initial heartbeat shortened to 15s for faster detect (30s for steady)
Closes CUB-233.