task-22(会话/菜单/权限): 定义 API 解包与错误归一化规则

envelope.ts 纯实现 unwrap(带 data 解包/success=false 抛错)、errorTextOf、
isUnauthorized(兼容 code/status/statusCode)、requestErrorMessage、loginRedirectTarget；
http.ts 复用 envelope 并对 HTTP200+code401 统一跳 /login?redirect=。

admin-frontend-vue/src/api/http.ts

@@ -0,0 +1,28 @@
+import axios from 'axios'
+import { isUnauthorized, loginRedirectTarget } from './envelope'
+
+export { unwrap } from './envelope'
+
+export const http = axios.create({
+  baseURL: '/',
+  withCredentials: true,
+  timeout: 30_000,
+})
+
+function redirectToLogin(): void {
+  if (typeof window === 'undefined') return
+  const target = loginRedirectTarget(window.location)
+  window.location.assign(`/login?redirect=${target}`)
+}
+
+http.interceptors.response.use(
+  (response) => {
+    // Java 未登录以 HTTP 200 + body.code=401 返回，需统一按未登录处理。
+    if (isUnauthorized(response.data)) redirectToLogin()
+    return response
+  },
+  (error) => {
+    if (error?.response?.status === 401 || isUnauthorized(error?.response?.data)) redirectToLogin()
+    return Promise.reject(error)
+  },
+)