vercel.json

{
  "version": 2,
  "builds": [
    { "src": "app_frontend.py", "use": "@vercel/python" },
    { "src": "app_backend.py", "use": "@vercel/python" }
  ],
  "routes": [
    { "src": "/upload", "dest": "app_backend.py" },
    { "src": "/filter", "dest": "app_backend.py" },
    { "src": "/export", "dest": "app_backend.py" },
    { "src": "/(.*)", "dest": "app_frontend.py" }
  ]
}