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/yallist/iterator.js

@@ -0,0 +1,8 @@
+'use strict'
+module.exports = function (Yallist) {
+  Yallist.prototype[Symbol.iterator] = function* () {
+    for (let walker = this.head; walker; walker = walker.next) {
+      yield walker.value
+    }
+  }
+}