Refactor code structure for improved readability and maintainability

Co-authored-by: Copilot <copilot@github.com>

flutter/lib/features/auth/data/auth_providers.dart

@@ -1,6 +1,7 @@
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import '../../../core/api/api_providers.dart';
 import '../../../core/platform/platform_providers.dart';
+import '../../../core/auth/jwt_decoder.dart';
 import 'auth_repository.dart';
 
 final authRepositoryProvider = Provider<AuthRepository>((ref) {
@@ -32,3 +33,9 @@ class AuthNotifier extends AsyncNotifier<String?> {
     state = const AsyncData(null);
   }
 }
+
+/// Synchronously derived provider — true when the current token has role == 'admin'.
+final isAdminProvider = Provider<bool>((ref) {
+  final token = ref.watch(authStateProvider).maybeWhen(data: (t) => t, orElse: () => null);
+  return jwtIsAdmin(token);
+});