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/mz/dns.js

@@ -0,0 +1,16 @@
+
+require('thenify-all').withCallback(
+  require('dns'),
+  exports, [
+    'lookup',
+    'resolve',
+    'resolve4',
+    'resolve6',
+    'resolveCname',
+    'resolveMx',
+    'resolveNs',
+    'resolveSrv',
+    'resolveTxt',
+    'reverse'
+  ]
+)