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

@@ -14,3 +14,9 @@ ZEP_API_KEY=your_zep_api_key_here
 LLM_BOOST_API_KEY=your_api_key_here
 LLM_BOOST_BASE_URL=your_base_url_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

@@ -1,9 +1,13 @@
-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({
+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: {
@@ -16,10 +20,11 @@ export default defineConfig({
       open: true,
       proxy: {
         '/api': {
-        target: 'http://localhost:5001',
+          target: backendUrl,
           changeOrigin: true,
           secure: false
         }
       }
     }
+  }
 })