feat: enhance authentication state management with model preloading

- Introduced a new private method `_preloadDefaultModel` to preload the default model upon successful authentication.
- Updated the token handling logic to kick off dependent background work, ensuring a smoother user experience.
- Enhanced error handling during model preloading to log failures appropriately.
- This change improves the efficiency of user data loading and prepares the application for subsequent operations.

lib/core/auth/auth_state_manager.dart

@@ -137,8 +137,9 @@ class AuthStateManager extends _$AuthStateManager {
             cache: true,
           );
 
-          // Update API service with token and load user data in background
+          // Update API service with token and kick off dependent background work
           _updateApiServiceToken(token);
+          _preloadDefaultModel();
           _loadUserData();
 
           // Background server validation; if it fails, invalidate token gracefully
@@ -257,8 +258,9 @@ class AuthStateManager extends _$AuthStateManager {
           cache: true,
         );
 
-        // Update API service with token
+        // Update API service with token and kick off dependent background work
         _updateApiServiceToken(tokenStr);
+        _preloadDefaultModel();
 
         // Load user data in background (consistent with credentials method)
         _loadUserData();
@@ -348,6 +350,7 @@ class AuthStateManager extends _$AuthStateManager {
       );
 
       _updateApiServiceToken(tokenStr);
+      _preloadDefaultModel();
 
       // Load user data in background
       _loadUserData();
@@ -584,6 +587,24 @@ class AuthStateManager extends _$AuthStateManager {
     }
   }
 
+  /// Preload the default model as soon as authentication succeeds.
+  void _preloadDefaultModel() {
+    Future.microtask(() async {
+      if (!ref.mounted) return;
+      try {
+        await ref.read(defaultModelProvider.future);
+        DebugLogger.auth('Default model preload requested');
+      } catch (e) {
+        if (!ref.mounted) return;
+        DebugLogger.warning(
+          'default-model-preload-failed',
+          scope: 'auth/state',
+          data: {'error': e.toString()},
+        );
+      }
+    });
+  }
+
   /// Load user data in background with JWT extraction fallback
   Future<void> _loadUserData() async {
     try {