fix(apps): consolidate FormzInput validators and fix login screen

- Move FormzInput validators to core/form_inputs/form_inputs.dart
- Fix login_screen.dart syntax error (missing 'class' keyword)
- Remove unused _isLoading field
- Fix unnecessary const keywords
- Update login_cubit and register_cubit imports
- Remove duplicate FormzInput definitions from register_cubit
- Add Toast and Banner UI feedback system
- Remove legacy login/register screens (login_code, login_email, login_password, register_step2)
- Remove unused warning_banner widget
- Update tests for new error messages and DI setup

apps/lib/core/di/injection.dart

@@ -12,17 +12,22 @@ import '../../features/auth/presentation/bloc/auth_bloc.dart';
 final sl = GetIt.instance;
 
 Future<void> configureDependencies() async {
+  if (sl.isRegistered<ApiClient>()) {
+    await sl.reset();
+  }
+
   final dio = Dio(BaseOptions(baseUrl: Env.apiUrl));
   final secureStorage = const FlutterSecureStorage();
   final tokenStorage = SecureTokenStorage(secureStorage);
 
-  sl.registerSingleton<Dio>(dio);
-  sl.registerSingleton<FlutterSecureStorage>(secureStorage);
-  sl.registerSingleton<TokenStorage>(tokenStorage);
-
-  final authApi = AuthApi(
-    ApiClient(baseUrl: Env.apiUrl, tokenStorage: tokenStorage, dio: dio),
+  final apiClient = ApiClient(
+    baseUrl: Env.apiUrl,
+    tokenStorage: tokenStorage,
+    dio: dio,
   );
+  sl.registerSingleton<ApiClient>(apiClient);
+
+  final authApi = AuthApi(apiClient);
   sl.registerSingleton<AuthApi>(authApi);
 
   final authRepository = AuthRepositoryImpl(
@@ -31,22 +36,14 @@ Future<void> configureDependencies() async {
   );
   sl.registerSingleton<AuthRepository>(authRepository);
 
-  sl.unregister<ApiClient>();
-  sl.registerSingleton<ApiClient>(
-    ApiClient(
-      baseUrl: Env.apiUrl,
-      tokenStorage: tokenStorage,
-      dio: dio,
-      refreshToken: (token) async {
-        try {
-          await authRepository.refresh(token);
-          return true;
-        } catch (_) {
-          return false;
-        }
-      },
-    ),
-  );
+  apiClient.setRefreshCallback((token) async {
+    try {
+      await authRepository.refresh(token);
+      return true;
+    } catch (_) {
+      return false;
+    }
+  });
 
   sl.registerSingleton<AuthBloc>(AuthBloc(authRepository));
 }