feat(antigravity): 支持 Refresh Token 批量导入创建 OAuth 账号

后端新增 ValidateRefreshToken service 方法和 POST /oauth/refresh-token 端点，
前端新增 API/Composable/UI 集成，OAuthAuthorizationFlow i18n 动态化，
支持在 Antigravity 创建账号时批量粘贴 Refresh Token 自动验证并创建账号。

frontend/src/api/admin/antigravity.ts

@@ -53,4 +53,18 @@ export async function exchangeCode(
   return data
 }
 
-export default { generateAuthUrl, exchangeCode }
+export async function refreshAntigravityToken(
+  refreshToken: string,
+  proxyId?: number | null
+): Promise<AntigravityTokenInfo> {
+  const payload: Record<string, any> = { refresh_token: refreshToken }
+  if (proxyId) payload.proxy_id = proxyId
+  
+  const { data } = await apiClient.post<AntigravityTokenInfo>(
+    '/admin/antigravity/oauth/refresh-token',
+    payload
+  )
+  return data
+}
+
+export default { generateAuthUrl, exchangeCode, refreshAntigravityToken }