test: 添加前端Vitest测试15项，覆盖安全修复验证

测试类:
- apiService.test.js (9项): P2-F2 admin token不回退、P2-C2 paymentNo移除、P2-C5 pageSize默认值
- loginRedirect.test.js (6项): P1-S5 Open Redirect校验

配置:
- 安装vitest/happy-dom/vue-test-utils
- vite.config.js添加test配置
- package.json添加test脚本

全部15项测试通过

frontend/vite.config.js

@@ -4,6 +4,10 @@ import { resolve } from 'path'
 
 export default defineConfig({
   plugins: [vue()],
+  test: {
+    environment: 'happy-dom',
+    globals: true
+  },
   resolve: {
     alias: {
       '@': resolve(__dirname, 'src')
@@ -11,6 +15,12 @@ export default defineConfig({
   },
   server: {
     port: 5173,
-    host: true
+    host: true,
+    proxy: {
+      '/api': {
+        target: 'http://localhost:8080',
+        changeOrigin: true
+      }
+    }
   }
 })