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/binary-extensions/index.d.ts

@@ -0,0 +1,14 @@
+/**
+List of binary file extensions.
+
+@example
+```
+import binaryExtensions = require('binary-extensions');
+
+console.log(binaryExtensions);
+//=> ['3ds', '3g2', …]
+```
+*/
+declare const binaryExtensions: readonly string[];
+
+export = binaryExtensions;