implemented a comprehensive client-side demo mode triggered by a "demo@" username prefix, serving curated fixture data for all app modules

lib/api/demo/data/demo_breaker.dart

@@ -0,0 +1,9 @@
+import '../../marianumconnect/queries/get_breakers/get_breakers_response.dart';
+
+/// Demo fixtures for the app-maintenance breaker.
+class DemoBreaker {
+  const DemoBreaker._();
+
+  /// No active rules — the demo app is never blocked.
+  static GetBreakersResponse none() => GetBreakersResponse([]);
+}