fix(auth): initialize demo user data on transition

Fixes a critical bug in the demo environment where authenticating as a new user (anonymous or via email) would fail.

Previously, when a new user was created, the `AppInitializer` would immediately try to fetch their settings and preferences. In the demo environment, this data did not exist yet, causing a `NotFoundException` that would halt the login process and leave the UI unresponsive.

This fix modifies `AppInitializer.handleUserTransition` to explicitly call `DemoDataInitializerService` for new users in the demo environment. This ensures that the necessary user data is created on-the-fly *before* any attempt is made to read it, resolving the race condition and allowing the authentication flow to complete successfully.

Author: fulleni

lib/app/services/app_initializer.dart

@@ -306,6 +306,23 @@ class AppInitializer {
     _logger.fine(
       '[AppInitializer] Re-fetching user data for transitioned user ${newUser.id}...',
     );
+
+    // --- Demo-Specific Logic: Initialize Data on Transition ---
+    // In demo mode, when a new user authenticates (e.g., anonymous sign-in
+    // or email verification), their user-specific data (settings, preferences)
+    // does not yet exist in the in-memory repositories. This block ensures
+    // that the DemoDataInitializerService is called to create this data
+    // *before* the subsequent code attempts to read it. This prevents a
+    // NotFoundException that would otherwise cause a critical error and
+    // stall the authentication flow.
+    if (_environment == local_config.AppEnvironment.demo) {
+      _logger.info(
+        '[AppInitializer] Demo mode: Initializing data for new user '
+        '${newUser.id} during transition.',
+      );
+      await demoDataInitializerService?.initializeUserSpecificData(newUser);
+    }
+
     try {
       final [
         userAppSettings as UserAppSettings?,