fix: read VITE_API_BASE_URL from .env for Vite dev proxy (fixes #480)

The Vite development proxy target was hardcoded to http://localhost:5001,
ignoring the VITE_API_BASE_URL environment variable that the axios client
already respects. This caused the dev proxy to still route to localhost even
when users configured a remote or custom backend address.

- Use loadEnv() in vite.config.js to read VITE_API_BASE_URL from the project
  root .env file and pass it as the proxy target (fallback: localhost:5001)
- Document VITE_API_BASE_URL in .env.example so users know the variable exists

.env.example

@@ -13,4 +13,10 @@ ZEP_API_KEY=your_zep_api_key_here
 # 注意如果不使用加速配置，env文件中就不要出现下面的配置项
 LLM_BOOST_API_KEY=your_api_key_here
 LLM_BOOST_BASE_URL=your_base_url_here
-LLM_BOOST_MODEL_NAME=your_model_name_here
+LLM_BOOST_MODEL_NAME=your_model_name_here
+
+# ===== 前端 / 部署配置（可选）=====
+# 后端 API 地址（axios 客户端 + Vite 开发代理均读取此变量）
+# 默认值：http://localhost:5001
+# 若后端运行在其他主机或端口，请取消注释并修改为对应地址
+# VITE_API_BASE_URL=http://localhost:5001

frontend/vite.config.js

@@ -1,24 +1,29 @@
-import { defineConfig } from 'vite'
+import { defineConfig, loadEnv } from 'vite'
 import vue from '@vitejs/plugin-vue'
 import path from 'path'
 
 // https://vite.dev/config/
-export default defineConfig({
-  plugins: [vue()],
-  resolve: {
-    alias: {
-      '@': path.resolve(__dirname, 'src'),
-      '@locales': path.resolve(__dirname, '../locales')
-    }
-  },
-  server: {
-    port: 3000,
-    open: true,
-    proxy: {
-      '/api': {
-        target: 'http://localhost:5001',
-        changeOrigin: true,
-        secure: false
+export default defineConfig(({ mode }) => {
+  const env = loadEnv(mode, path.resolve(__dirname, '..'), '')
+  const backendUrl = env.VITE_API_BASE_URL || 'http://localhost:5001'
+
+  return {
+    plugins: [vue()],
+    resolve: {
+      alias: {
+        '@': path.resolve(__dirname, 'src'),
+        '@locales': path.resolve(__dirname, '../locales')
+      }
+    },
+    server: {
+      port: 3000,
+      open: true,
+      proxy: {
+        '/api': {
+          target: backendUrl,
+          changeOrigin: true,
+          secure: false
+        }
       }
     }
   }