feat: Add presence heartbeat for Matrix online status

- matrix-gateway: POST /internal/matrix/presence/online endpoint
- usePresenceHeartbeat hook with activity tracking
- Auto away after 5 min inactivity
- Offline on page close/visibility change
- Integrated in MatrixChatRoom component

services/node-registry/requirements.txt

@@ -8,3 +8,4 @@ sqlalchemy[asyncio]==2.0.36
 alembic==1.14.0
 python-json-logger==3.2.1
 prometheus-client==0.21.0
+psycopg2-binary>=2.9.0