Vercel deploy: CLI once, then just push

0. Preconditions

• A GitHub repo exists (github-push skill). If not, do that first.
• npm run build passes locally. Always run it once before deploying. An error here is an error on Vercel.

1. Login (once)

npm i -g vercel
vercel login

The browser opens; log in with the GitHub account. If Windows cannot find vercel, open a new terminal.

2. First deploy