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

lib/api/marianumconnect/auth/session_validator.dart

@@ -14,6 +14,9 @@ class SessionValidator {
     required Future<void> Function() onInvalidated,
   }) async {
     if (!AccountData().isPopulated()) return;
+    // AuthVerify uses its own dio (bypassing the demo interceptor), so a demo
+    // session must be skipped here or its missing token would 401 into a logout.
+    if (AccountData().isDemo) return;
     final username = AccountData().getUsername();
     final password = AccountData().getPassword();
     try {

lib/api/marianumconnect/marianumconnect_api.dart

@@ -1,5 +1,6 @@
 import 'package:dio/dio.dart';
 
+import '../demo/demo_marianumconnect_interceptor.dart';
 import 'auth/auth_interceptor.dart';
 
 /// Singleton dio instance for the Marianum-Connect mobile API. Wired with the
@@ -24,6 +25,7 @@ class MarianumConnectApi {
         contentType: 'application/json',
       ),
     );
+    dio.interceptors.add(DemoMarianumConnectInterceptor());
     dio.interceptors.add(MarianumConnectAuthInterceptor());
     return dio;
   }