build(frontend): vite 加载开发环境变量

- 使用 loadEnv 读取 VITE_DEV_PROXY_TARGET/VITE_DEV_PORT
- 注入 public settings 与 dev proxy 使用同源后端地址

frontend/vite.config.ts

-import { defineConfig, Plugin } from 'vite'
+import { defineConfig, loadEnv, Plugin } from 'vite'
 import vue from '@vitejs/plugin-vue'
 import checker from 'vite-plugin-checker'
 import { resolve } from 'path'
@@ -7,9 +7,7 @@ import { resolve } from 'path'
  * Vite 插件：开发模式下注入公开配置到 index.html
  * 与生产模式的后端注入行为保持一致，消除闪烁
  */
-function injectPublicSettings(): Plugin {
-  const backendUrl = process.env.VITE_DEV_PROXY_TARGET || 'http://localhost:8080'
-
+function injectPublicSettings(backendUrl: string): Plugin {
   return {
     name: 'inject-public-settings',
     transformIndexHtml: {
@@ -35,14 +33,20 @@ function injectPublicSettings(): Plugin {
   }
 }
 
-export default defineConfig({
+export default defineConfig(({ mode }) => {
+  // 加载环境变量
+  const env = loadEnv(mode, process.cwd(), '')
+  const backendUrl = env.VITE_DEV_PROXY_TARGET || 'http://localhost:8080'
+  const devPort = Number(env.VITE_DEV_PORT || 3000)
+
+  return {
     plugins: [
       vue(),
       checker({
         typescript: true,
         vueTsc: true
       }),
-    injectPublicSettings()
+      injectPublicSettings(backendUrl)
     ],
   resolve: {
     alias: {
@@ -104,16 +108,17 @@ export default defineConfig({
   },
     server: {
       host: '0.0.0.0',
-    port: Number(process.env.VITE_DEV_PORT || 3000),
+      port: devPort,
       proxy: {
         '/api': {
-        target: process.env.VITE_DEV_PROXY_TARGET || 'http://localhost:8080',
+          target: backendUrl,
           changeOrigin: true
         },
         '/setup': {
-        target: process.env.VITE_DEV_PROXY_TARGET || 'http://localhost:8080',
+          target: backendUrl,
           changeOrigin: true
         }
       }
     }
+  }
 })