When running inside Docker with the CMS_ALIAS environment variable set to a subdirectory path (e.g., /xibo), the layout preview and thumbnails fail to load correctly.

• Layout preview shows a black page.
• Clicking preview pop-out results in a blank page.
• Thumbnails for layouts are not showing anything.

Environment:

• CMS versions tested: Version 4.3.0-alpha
• Using CMS_ALIAS=/xibo in docker-compose environment

Steps to Reproduce:

1. Install v4 with Docker and set CMS_ALIAS=/xibo
2. Access layout preview or thumbnails via CMS UI
3. Observe blank/black preview screen and missing thumbnails