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

backend/domain/user/types.ts

@@ -0,0 +1,14 @@
+/**
+ * Domain types for User
+ */
+
+export type UserRole = 'owner' | 'admin' | 'member' | 'guest' | 'agent';
+
+export interface User {
+  userId: string;
+  email?: string;
+  name?: string;
+  roles?: UserRole[];
+}
+
+