fix(groups): 用户分组不下发内部路由信息

- 普通用户 Group DTO 移除 model_routing/account_count/account_groups，避免泄露内部路由与账号信息\n- 新增 AdminGroup DTO，并仅在管理员分组接口返回完整字段\n- 前端拆分 Group/AdminGroup，管理端页面与 API 使用 AdminGroup\n- 增加 /api/v1/groups/available 契约测试，防止回归

frontend/src/components/account/CreateAccountModal.vue

@@ -1816,7 +1816,7 @@ import {
 import { useOpenAIOAuth } from '@/composables/useOpenAIOAuth'
 import { useGeminiOAuth } from '@/composables/useGeminiOAuth'
 import { useAntigravityOAuth } from '@/composables/useAntigravityOAuth'
-import type { Proxy, Group, AccountPlatform, AccountType } from '@/types'
+import type { Proxy, AdminGroup, AccountPlatform, AccountType } from '@/types'
 import BaseDialog from '@/components/common/BaseDialog.vue'
 import Icon from '@/components/icons/Icon.vue'
 import ProxySelector from '@/components/common/ProxySelector.vue'
@@ -1862,7 +1862,7 @@ const apiKeyHint = computed(() => {
 interface Props {
   show: boolean
   proxies: Proxy[]
-  groups: Group[]
+  groups: AdminGroup[]
 }
 
 const props = defineProps<Props>()