[UVE]: Theme Selector Does Not Show Themes from Other Sites in Layout Editor

Problem Statement

When editing a page in the Layout Editor (UVE), the Theme Selector does not show available themes from other sites. This blocks users from reusing shared styling assets across multi-site environments.

Steps to Reproduce

1. Create a new blank site and add a new page.
2. Open the page in the Layout Editor (UVE).
3. Click on Layout > Theme.
4. Observe that no themes are shown, even if other themes exist on different sites.

Expected Behavior

• The Theme Selector should list themes available across all sites (unless explicitly restricted).
• Editors should be able to apply cross-site themes when styling a page.

Acceptance Criteria

• Themes from all sites are visible and selectable in the Theme Selector.
• Theme application works correctly, regardless of where the theme is defined.
• Any site-scoping rules are respected but clearly surfaced (e.g., labels, filters).

dotCMS Version

main / trunk

Proposed Objective

User Experience

Proposed Priority

Priority 2 – Important

Start by reproducing the issue in the UVE through Layout > Theme on a blank site, then trace how the Theme Selector loads themes and applies site-scoping rules. Done means themes from other sites are visible and selectable, application works across sites, and any restrictions are clearly surfaced.