The root README was a design handoff for a prototype that is not in this repo,
web-player/README.md was the sv template, and deploy/README.md only covered
development. Replace all three and document the production deploy: its
prerequisites, what up.sh does and why nginx sits in front.
The docs under docs/ still used the pre-monorepo project paths, Ardalis.Result
instead of ErrorOr and the player.html test console that no longer exists.
Updates the compose build context, the Dockerfile header, the package
name and the docs. The compose service and container keep the name
frontend/musify-frontend, since nginx routes to http://frontend:3000.
The source files also carry the first prettier pass, so the rename and
the reformat land together for them.