feat: support cross-origin deployment with VITE_API_BASE_URL

- Set VITE_API_BASE_URL=https://opinion-api.moreminimore.com for
  frontend-backend split deployment
- Vite proxy also uses API_BACKEND_URL env var as target
- Falls back to same-origin proxy for local dev

frontend/src/api/index.js

@@ -2,6 +2,9 @@ import axios from 'axios'
 import i18n from '../i18n'
 
 // 创建axios实例
+// VITE_API_BASE_URL: set to backend URL for cross-origin deployments
+//   e.g. https://opinion-api.moreminimore.com
+//   Falls back to '' (empty) when using vite proxy (same-origin / local dev)
 const service = axios.create({
   baseURL: import.meta.env.VITE_API_BASE_URL || '',
   timeout: 300000, // 5分钟超时（本体生成可能需要较长时间）