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/living-map-service/requirements.txt

@@ -0,0 +1,9 @@
+fastapi==0.104.1
+uvicorn==0.24.0
+pydantic==2.5.0
+asyncpg==0.29.0
+httpx==0.25.1
+python-dotenv==1.0.0
+nats-py==2.6.0
+websockets==12.0
+