fix: Update start script to use PORT 3000 for consistency (#23)

Co-authored-by: rikasai233 <rikasai233@gmail.com>

Author: lihuacai168

frontend/package.json

@@ -22,7 +22,7 @@
     "web-vitals": "^2.1.4"
   },
   "scripts": {
-    "start": "PORT=3001 react-scripts start",
+    "start": "PORT=3000 react-scripts start",
     "build": "react-scripts build",
     "test": "react-scripts test",
     "eject": "react-scripts eject"