Dev and prod on Amplify branches

Two Amplify environments mapped to two branches: main deploys dev, prod deploys prod, and promotion is a merge. A short helper document lists the order of operations and the one command that must not run against the wrong environment.

For a two-person project this is the whole release process, and it is enough. The rule the document exists for: the Amplify environment checked out must match the branch you are on, dev on main and prod on prod, because the CLI deploys whichever environment is checked out.