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/eslint/messages/failed-to-read-json.js

@@ -0,0 +1,11 @@
+"use strict";
+
+module.exports = function(it) {
+    const { path, message } = it;
+
+    return `
+Failed to read JSON file at ${path}:
+
+${message}
+`.trimStart();
+};