Add api/index.py for Vercel serverless function and update frontend endpoint

Fix: Remove workspace config and regenerate package-lock.json with Vite 5.x

Regenerate package-lock.json with stable Vite 5.x dependencies

Downgrade to stable Vite 5.x and React 18.x for Vercel compatibility

Remove TypeScript build check to fix Vercel build

Deploy to Vercel: Add serverless functions, frontend, and deployment docs