feat: add cross-platform start.sh script and update package.json for macOS/Linux

frontend/package.json

@@ -3,7 +3,7 @@
   "version": "0.1.0",
   "private": true,
   "scripts": {
-    "dev": "concurrently --names \"NEXT,API\" --prefix-colors \"cyan,yellow\" \"next dev\" \"cd ../backend && venv\\Scripts\\python.exe main.py\"",
+    "dev": "concurrently \"npm run dev:frontend\" \"cd ../backend && python -m uvicorn main:app --reload\"",
     "dev:frontend": "next dev",
     "dev:backend": "cd ../backend && venv\\Scripts\\python.exe main.py",
     "build": "next build",
@@ -37,4 +37,4 @@
     "tailwindcss": "^4",
     "typescript": "^5"
   }
-}
+}