The 'api' mode is being renamed to 'headless' to better reflect its
purpose: serving the API without the admin UI. This change aligns with
the existing framework concept of a headless backend.
The 'standalone' mode is renamed to 'admin' to indicate that it serves
both the API and the admin UI.
Rename the web adapter to universal adapter to better reflect its
framework-agnostic nature. This change involves updating package.json,
file paths, and documentation.