Translate all of docs/ from Spanish to English and rewrite the root
README as a short project overview instead of a technical run guide.
Remove web-player/design_handoff_musify_player, an old design-tool
export that was no longer needed.
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.