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/api/api_exception.dart

@@ -1,3 +1,5 @@
+import 'package:dio/dio.dart';
+
 abstract class ApiException implements Exception {
   final String message;
   final int? statusCode;
@@ -6,12 +8,58 @@ abstract class ApiException implements Exception {
 
   factory ApiException.fromDioError(Object error) {
     if (error is ApiException) return error;
-    return ServerException('Request failed: ${error.toString()}');
-  }
-}
+    if (error is DioException) {
+      final response = error.response;
+      final statusCode = response?.statusCode;
+      final data = response?.data;
 
-class NetworkException extends ApiException {
-  const NetworkException(super.message);
+      String detail;
+      if (data is Map<String, dynamic>) {
+        detail =
+            (data['detail'] ?? data['message'] ?? data['error'])?.toString() ??
+            '请求失败';
+      } else {
+        detail = '请求失败';
+      }
+
+      final localized = _localizeError(detail, statusCode);
+
+      if (statusCode == 401) {
+        return UnauthorizedException(localized);
+      }
+      if (statusCode == 422) {
+        return ValidationException(
+          localized,
+          errors: data,
+          statusCode: statusCode,
+        );
+      }
+      return ServerException(localized, statusCode: statusCode);
+    }
+    return const ServerException('网络错误');
+  }
+
+  static String _localizeError(String detail, int? statusCode) {
+    if (statusCode == 401) {
+      return '邮箱或密码错误';
+    }
+    if (statusCode == 403) {
+      return '没有权限执行此操作';
+    }
+    if (statusCode == 404) {
+      return '请求的资源不存在';
+    }
+    if (statusCode == 429) {
+      return '请求过于频繁，请稍后再试';
+    }
+    if (statusCode != null && statusCode >= 500) {
+      return '服务器错误，请稍后再试';
+    }
+    if (detail.contains('credentials') || detail.contains('password')) {
+      return '邮箱或密码错误';
+    }
+    return detail;
+  }
 }
 
 class ServerException extends ApiException {
@@ -19,7 +67,7 @@ class ServerException extends ApiException {
 }
 
 class UnauthorizedException extends ApiException {
-  const UnauthorizedException([super.message = 'Authentication required'])
+  const UnauthorizedException([super.message = '请重新登录'])
     : super(statusCode: 401);
 }