refactor: 清理站内导航死代码 (删除孤立NavigationPage组件+navigationApi+导航mock数据)

- 删除 frontend/src/components/navigation/NavigationPage.tsx (359行, 菜单/路由移除后遗留的孤立组件)
- 移除 services/api.ts 中 navigationApi (唯一消费者已删除)
- 移除 mocks/modules/misc.ts 中 navigationGroups/navigationLinks 死数据 (252行)
- 清理 mocks/data.ts barrel 中导航 re-export
- 修正 cloud.ts 误导性注释 (站内导航→云平台/账号/区域/域名数据)
- 后端 navigation.go 保留不动 (菜单已移除但后端代码保留)
- tsc --noEmit 零错误 + npm run build 通过

frontend/src/services/api.ts

@@ -376,37 +376,6 @@ export const approvalApi = {
   },
 };
 
-// ==================== 导航管理 API ====================
-export const navigationApi = {
-  getGroups: async () => {
-    return http.get('/navigations/groups');
-  },
-  createGroup: async (data: any) => {
-    return http.post('/navigations/groups', data);
-  },
-  updateGroup: async (id: number | string, data: any) => {
-    return http.put(`/navigations/groups/${id}`, data);
-  },
-  deleteGroup: async (id: number | string) => {
-    return http.delete(`/navigations/groups/${id}`);
-  },
-  getLinks: async () => {
-    return http.get('/navigations/links');
-  },
-  createLink: async (data: any) => {
-    return http.post('/navigations/links', data);
-  },
-  updateLink: async (id: number | string, data: any) => {
-    return http.put(`/navigations/links/${id}`, data);
-  },
-  deleteLink: async (id: number | string) => {
-    return http.delete(`/navigations/links/${id}`);
-  },
-  toggleFavorite: async (id: number | string) => {
-    return http.post(`/navigations/links/${id}/favorite`);
-  },
-};
-
 // ==================== 云管理 API ====================
 export const cloudApi = {
   getAccounts: async () => {