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/reusify/reusify.js

@@ -0,0 +1,33 @@
+'use strict'
+
+function reusify (Constructor) {
+  var head = new Constructor()
+  var tail = head
+
+  function get () {
+    var current = head
+
+    if (current.next) {
+      head = current.next
+    } else {
+      head = new Constructor()
+      tail = head
+    }
+
+    current.next = null
+
+    return current
+  }
+
+  function release (obj) {
+    tail.next = obj
+    tail = obj
+  }
+
+  return {
+    get: get,
+    release: release
+  }
+}
+
+module.exports = reusify