Add frontend PORT env config and remove package-lock.json from repo

- Add PORT=3002 to frontend .env.example
- Use dotenv-cli to load env vars for next dev/start
- Add package-lock.json to .gitignore and remove from tracking

frontend/.env.example

@@ -1,3 +1,6 @@
+# Frontend port (dev/start)
+PORT=3002
+
 # API URL (leave empty for same-origin proxy)
 NEXT_PUBLIC_API_URL=
 

frontend/package.json

@@ -3,9 +3,9 @@
   "version": "1.0.0",
   "private": true,
   "scripts": {
-    "dev": "next dev -p 3002",
+    "dev": "dotenv -e .env -- next dev",
     "build": "next build",
-    "start": "next start -p 3002",
+    "start": "dotenv -e .env -- next start",
     "lint": "next lint"
   },
   "dependencies": {
@@ -25,6 +25,7 @@
     "@types/react": "^18.3.3",
     "@types/react-dom": "^18.3.0",
     "autoprefixer": "^10.4.19",
+    "dotenv-cli": "^11.0.0",
     "postcss": "^8.4.38",
     "tailwindcss": "^3.4.4",
     "typescript": "^5.5.2"