feat: Build the pages with Display Builder instead of a long WYSIWYG body

Problem/Motivation

The demo pages of the site template carry their whole layout as UIkit markup inside one long WYSIWYG body. Editors cannot rearrange that layout, and it hides the theme's own components.

Steps to reproduce

1. Install the site template and open one of its demo pages for editing.
2. See the whole layout sitting in a single WYSIWYG body field.

Proposed resolution

Build each page as a Display Builder page layout made of the theme components (section, grid, heading, card, switcher, accordion, button). Keep the page body empty, mark the content section as the main landmark, and let the text parts of a page keep their images.

Remaining tasks

• ✅ 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

User interface changes

• Demo pages render as Display Builder page layouts instead of one WYSIWYG body.

API changes

• N/A

Data model changes

• N/A

Release notes snippet

• Demo pages are now built with Display Builder instead of a single WYSIWYG body.

AI-Generated: Yes