feat: 实现前端卡密管理界面

- 卡密列表展示与分页功能

- 单个/批量创建卡密

- 卡密删除与批量删除

- 卡密导出功能 (file-saver)

- 启用/禁用状态切换

- 状态判断 (有效/已使用/已失效)

- Toast 通知系统 (vue-sonner)

- 登录页面错误提示优化

- 后端登录错误消息中文化

frontend/src/api/request.ts

@@ -0,0 +1,42 @@
+import axios, { type InternalAxiosRequestConfig, type AxiosResponse, type AxiosError } from 'axios'
+import { useAuthStore } from '@/stores/auth'
+import router from '@/router'
+
+const request = axios.create({
+    baseURL: import.meta.env.VITE_BASE_URL || '',
+    timeout: 30000,
+    headers: {
+        'Content-Type': 'application/json',
+    },
+})
+
+// Request interceptor - add Authorization header
+request.interceptors.request.use(
+    (config: InternalAxiosRequestConfig) => {
+        const authStore = useAuthStore()
+        if (authStore.token) {
+            config.headers.Authorization = `Bearer ${authStore.token}`
+        }
+        return config
+    },
+    (error: AxiosError) => {
+        return Promise.reject(error)
+    }
+)
+
+// Response interceptor - handle 401/403
+request.interceptors.response.use(
+    (response: AxiosResponse) => {
+        return response
+    },
+    (error: AxiosError) => {
+        if (error.response?.status === 401 || error.response?.status === 403) {
+            const authStore = useAuthStore()
+            authStore.logout()
+            router.push('/admin/login')
+        }
+        return Promise.reject(error)
+    }
+)
+
+export default request