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

node_modules/@babel/traverse/tsconfig.overrides.json

@@ -0,0 +1,6 @@
+{
+  "compilerOptions": {
+    "strictNullChecks": true,
+    "strictPropertyInitialization": true
+  }
+}