feat: Build the WebAPI Starter site template on 1.0.x

Problem/Motivation

There is no basic Drupal API site template. The WebAPI Starter project is empty, so the installer has nothing to offer for a plain API site.

Proposed resolution

Build the site template on a new 1.0.x branch, as a standalone recipe of type Site.

• Keeps the standard Drupal content model, and adds Web API on top of it.
• JSON:API served from /api, and read-only. Write operations stay a decision for the site owner.
• OAuth 2.0 with consumers, HTTP Basic authentication, and the OpenAPI documents rendered with Swagger UI at /api-docs.
• The Drupal core administration theme is the default theme, for the back end and the front end.
• Registration is closed: an administrator creates the accounts.

The site template is standalone: it never requires or applies another site template. Only packages from drupal.org.

Remaining tasks

• ✅ Build the site template on 1.0.x
• ❌ Review the merge request
• ❌ Release 1.0.0

Release notes snippet

WebAPI Starter 1.0.0: the basic Drupal API site template, with JSON:API from /api and Swagger UI documentation.

AI-Generated: Yes