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/resolve/test/resolver/baz/package.json

@@ -0,0 +1,4 @@
+{
+    "name": "baz",
+    "main": "quux.js"
+}

node_modules/resolve/test/resolver/baz/quux.js

@@ -0,0 +1 @@
+module.exports = 1;