feat(frontend): 对接后端统一响应格式，增强错误处理

- 新增 types/api.ts，定义 ApiResponse/PaginatedData 泛型类型和业务错误码常量
- 增强 request.ts 拦截器：提取后端错误信息、映射 HTTP 状态码和业务错误码为中文提示
- 为 auth/audit/subsystem API 添加泛型返回类型
- 为各视图添加 try/catch 防止未处理的 Promise 拒绝

frontend/src/api/request.ts

@@ -1,6 +1,8 @@
-import axios from 'axios'
+import axios, { type AxiosResponse, type AxiosError } from 'axios'
 import { getToken, removeToken } from '@/utils/auth'
 import { ElMessage } from 'element-plus'
+import type { ApiResponse } from '@/types/api'
+import { codeMessageMap } from '@/types/api'
 
 const request = axios.create({
   baseURL: '/api/v1',
@@ -21,22 +23,55 @@ request.interceptors.request.use(
   }
 )
 
+/** HTTP 状态码对应的用户友好提示 */
+const httpMessageMap: Record<number, string> = {
+  400: '请求参数错误',
+  401: '未授权，请重新登录',
+  403: '没有权限执行此操作',
+  404: '请求的资源不存在',
+  408: '请求超时，请稍后重试',
+  500: '服务器内部错误',
+  502: '网关错误',
+  503: '服务暂时不可用，请稍后重试',
+}
+
+/** 根据后端错误码获取用户友好提示 */
+function getBusinessMessage(code: number, fallback?: string): string {
+  return codeMessageMap[code] || fallback || '请求失败'
+}
+
 // 响应拦截器
 request.interceptors.response.use(
-  (response) => {
+  (response: AxiosResponse<ApiResponse>) => {
     const { data } = response
     if (data.code !== 0) {
-      ElMessage.error(data.message || '请求失败')
-      return Promise.reject(new Error(data.message))
+      const message = getBusinessMessage(data.code, data.message)
+      ElMessage.error(message)
+      return Promise.reject(new Error(message))
     }
-    return data
+    return data as any
   },
-  (error) => {
-    if (error.response?.status === 401) {
-      removeToken()
-      window.location.href = '/login'
+  (error: AxiosError<ApiResponse>) => {
+    // 优先使用后端返回的错误信息
+    const backendMessage = error.response?.data?.message
+
+    if (error.response) {
+      const status = error.response.status
+
+      if (status === 401) {
+        removeToken()
+        window.location.href = '/login'
+        ElMessage.error(backendMessage || '未授权，请重新登录')
+      } else {
+        const message = backendMessage || httpMessageMap[status] || `请求失败 (${status})`
+        ElMessage.error(message)
+      }
+    } else if (error.code === 'ECONNABORTED') {
+      ElMessage.error('请求超时，请检查网络后重试')
+    } else {
+      ElMessage.error('网络连接异常，请检查网络')
     }
-    ElMessage.error(error.message || '网络错误')
+
     return Promise.reject(error)
   }
 )