chore: add demo profile and local api proxy

README.md

@@ -25,6 +25,15 @@ mvn test
 - Rider H5: `http://localhost:5174`
 - Resident miniapp: open `miniapp/project.config.json` in WeChat DevTools
 
+No-database demo backend:
+
+```powershell
+cd backend
+mvn spring-boot:run "-Dspring-boot.run.profiles=demo"
+```
+
+Demo profile URL: `http://localhost:18080`
+
 Demo accounts:
 
 - Admin: `admin / admin123`