feat(admin): 添加管理员直接修改用户 API Key 分组的功能

- 新增 PUT /api/v1/admin/api-keys/:id 端点，允许管理员修改任意用户 API Key 的分组绑定
- 跳过用户级权限校验但保留分组有效性验证，修改后触发认证缓存失效
- Service 层支持三态语义：nil=不修改，0=解绑，>0=绑定，<0=拒绝
- 指针值拷贝保证安全隔离，负数 groupID 返回 400 INVALID_GROUP_ID
- 前端 UserApiKeysModal 新增可点击的分组选择下拉框，支持多 Key 并发更新
- 下拉支持视口翻转和滚动关闭，按钮有 disabled 和加载状态
- 覆盖：后端 20 个单元测试 (Service 11 + Handler 9) + 前端 16 个 E2E 测试
- golangci-lint 0 issues, make test-unit 全部通过

frontend/src/api/admin/apiKeys.ts

@@ -0,0 +1,26 @@
+/**
+ * Admin API Keys API endpoints
+ * Handles API key management for administrators
+ */
+
+import { apiClient } from '../client'
+import type { ApiKey } from '@/types'
+
+/**
+ * Update an API key's group binding
+ * @param id - API Key ID
+ * @param groupId - Group ID (0 to unbind, positive to bind, null/undefined to skip)
+ * @returns Updated API key
+ */
+export async function updateApiKeyGroup(id: number, groupId: number | null): Promise<ApiKey> {
+  const { data } = await apiClient.put<ApiKey>(`/admin/api-keys/${id}`, {
+    group_id: groupId === null ? 0 : groupId
+  })
+  return data
+}
+
+export const apiKeysAPI = {
+  updateApiKeyGroup
+}
+
+export default apiKeysAPI

frontend/src/api/admin/index.ts

@@ -21,6 +21,7 @@ import userAttributesAPI from './userAttributes'
 import opsAPI from './ops'
 import errorPassthroughAPI from './errorPassthrough'
 import dataManagementAPI from './dataManagement'
+import apiKeysAPI from './apiKeys'
 
 /**
  * Unified admin API object for convenient access
@@ -43,7 +44,8 @@ export const adminAPI = {
   userAttributes: userAttributesAPI,
   ops: opsAPI,
   errorPassthrough: errorPassthroughAPI,
-  dataManagement: dataManagementAPI
+  dataManagement: dataManagementAPI,
+  apiKeys: apiKeysAPI
 }
 
 export {
@@ -64,7 +66,8 @@ export {
   userAttributesAPI,
   opsAPI,
   errorPassthroughAPI,
-  dataManagementAPI
+  dataManagementAPI,
+  apiKeysAPI
 }
 
 export default adminAPI