feat: Add proxy to frontend dev server to fix CORS issues

sau_frontend/.env.development

@@ -2,7 +2,7 @@
 NODE_ENV=development
 
 # API 基础地址
-VITE_API_BASE_URL=http://localhost:5409
+VITE_API_BASE_URL=/api
 
 # 应用端口
 VITE_PORT=5173

sau_frontend/vite.config.js

@@ -19,7 +19,14 @@ export default defineConfig({
   },
   server: {
     port: 5173,
-    open: true
+    open: true,
+    proxy: {
+      '/api': {
+        target: 'http://localhost:5409',
+        changeOrigin: true,
+        rewrite: (path) => path.replace(/^\/api/, '')
+      }
+    }
   },
   build: {
     outDir: 'dist',