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/vite.config.js

@@ -18,9 +18,9 @@ export default defineConfig({
     allowedHosts: true,
     proxy: {
       '/api': {
-        target: 'http://localhost:5001',
+        target: process.env.API_BACKEND_URL || 'http://localhost:5001',
         changeOrigin: true,
-        secure: false
+        secure: true
       }
     }
   }