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/update-browserslist-db/index.d.ts

@@ -0,0 +1,6 @@
+/**
+ * Run update and print output to terminal.
+ */
+declare function updateDb(print?: (str: string) => void): void
+
+export = updateDb