feat: #3626274 Use the UIkit themes for the site and the back office

UI Suite UIkit becomes the default theme and UIkit Admin the administration theme, instead of Default Admin for the whole site, as the other Webship site templates do.

Issue: https://www.drupal.org/project/webapi_starter/issues/3626274

• Install the UI Suite modules, ui_suite_uikit and uikit_admin, and import their block placements.
• Require drupal/ui_suite_uikit: ^1.0 and drupal/uikit_admin: ~4.0.
• README, AGENTS.md and the recipe description name the UIkit themes.
• Proven with a fresh install from webships_project (drush site:install ../recipes/webapi_starter): default ui_suite_uikit, admin uikit_admin, the pages answer 200, no errors in the log.

AI-Generated: Yes

Checkpoints

• File an issue
• Addition for a new supported feature
• Testing to ensure no regression
• Documentation
• CI pipeline green
• Release