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-network-app/node_modules/react/cjs/react.shared-subset.development.js

@@ -0,0 +1,20 @@
+/**
+ * @license React
+ * react.shared-subset.development.js
+ *
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+'use strict';
+
+if (process.env.NODE_ENV !== "production") {
+  (function() {
+'use strict';
+
+// eslint-disable-next-line react-internal/prod-error-codes
+throw new Error('This entry point is not yet supported outside of experimental channels');
+  })();
+}