feat(auth): refactor token retrieval to use maybeWhen for improved null handling

flutter/lib/features/import/presentation/recipe_import_tab.dart

@@ -50,7 +50,6 @@ class _RecipeImportTabState extends ConsumerState<RecipeImportTab> {
     if (result == null || result.files.isEmpty) return;
     setState(() {
       _pickedFile = result.files.first;
-      _error = null;
     });
   }
 
@@ -65,7 +64,10 @@ class _RecipeImportTabState extends ConsumerState<RecipeImportTab> {
     setState(() => _isLoading = true);
 
     try {
-      final token = ref.read(authStateProvider).valueOrNull ??
+      final token = ref.read(authStateProvider).maybeWhen(
+        data: (t) => t,
+        orElse: () => null,
+          ) ??
           await ref.read(authStateProvider.future);
       final repo = ref.read(importRepositoryProvider);
       final result = _method == _Method.file