feat: #3622691 Add the UIkit showcase and install without Layout Builder

Adds a UIkit showcase to the demo content and drops the Layout Builder dependency from install.

• New showcase pages (/welcome, Features, Get started, Gallery, Slideshows, Elements, Support, Image credits) plus 8 Web Blog posts, using UIkit demo images (MIT) and NASA public domain photos as media, with a "UIkit showcase" menu and footer links. Front page stays the blog listing.
• Install without Layout Builder: core Standard and drupal_cms_admin_ui are no longer included as recipes (they pull in Navigation/Dashboard, which need Layout Builder); their needed settings are copied into recipe.yml, and the admin UI modules are required directly in composer.json.
• Fixes the video field extra-field action to use setSettings so the demo video imports.
• Tests updated for the new content (32 blog posts → 4 pages, showcase pages published, showcase components); a fresh drush site:install from the recipe passes all webship-js tests, with layout_builder/navigation/dashboard not installed.

Related to #3622679 (default dashboards), which needs Layout Builder — flagged on the issue for maintainers to reconcile, no change made there.

Issue: https://www.drupal.org/project/website_starter/issues/3622691

AI-Generated: Yes

Checkpoints

• File an issue about this project
• Addition/Change/Update/Fix to this project
• Testing to ensure no regression
• Automated unit/functional testing coverage
• Developer Documentation support on feature change/addition
• User Guide Documentation support on feature change/addition
• UX/UI designer responsibilities
• Accessibility and Readability
• Reviewed by a human
• Code review by maintainers
• Full testing and approval
• Credit contributors
• Review with the product owner
• Update Release Notes
• Release