fix(gateway): 自定义错误码触发停止调度

- 修改 HandleUpstreamError 逻辑，启用自定义错误码时所有在列表中的错误码都会停止调度
- 添加 handleCustomErrorCode 函数处理自定义错误码的账号停用
- 前端添加 429/529 错误码的警告提示，因为这些错误码已有内置处理机制
- 更新 EditAccountModal、CreateAccountModal、BulkEditAccountModal 的错误码添加逻辑

frontend/src/i18n/locales/en.ts

@@ -1203,6 +1203,10 @@ export default {
       customErrorCodesHint: 'Only stop scheduling for selected error codes',
       customErrorCodesWarning:
         'Only selected error codes will stop scheduling. Other errors will return 500.',
+      customErrorCodes429Warning:
+        '429 already has built-in rate limit handling. Adding it to custom error codes will disable the account instead of temporary rate limiting. Are you sure?',
+      customErrorCodes529Warning:
+        '529 already has built-in overload handling. Adding it to custom error codes will disable the account instead of temporary overload marking. Are you sure?',
       selectedErrorCodes: 'Selected',
       noneSelectedUsesDefault: 'None selected (uses default policy)',
       enterErrorCode: 'Enter error code (100-599)',

frontend/src/i18n/locales/zh.ts

@@ -1339,6 +1339,10 @@ export default {
       customErrorCodes: '自定义错误码',
       customErrorCodesHint: '仅对选中的错误码停止调度',
       customErrorCodesWarning: '仅选中的错误码会停止调度，其他错误将返回 500。',
+      customErrorCodes429Warning:
+        '429 已有内置的限流处理机制。添加到自定义错误码后，将直接停止调度而非临时限流。确定要添加吗？',
+      customErrorCodes529Warning:
+        '529 已有内置的过载处理机制。添加到自定义错误码后，将直接停止调度而非临时标记过载。确定要添加吗？',
       selectedErrorCodes: '已选择',
       noneSelectedUsesDefault: '未选择（使用默认策略）',
       enterErrorCode: '输入错误码 (100-599)',