Issue-13: convert templates/layouts from static files to custom post type

[mogmarsh]

Description

This PR converts templates/layouts from static files to a custom post type. It updates all references to the static files and file names to use the new custom post type, pulling from the REST API or WP_Query as appropriate.

Changes

• Created a custom post type for templates/layouts
• Updated all references to static files and file names to use the new custom post type
• Replaced static file storage with REST API or WP_Query calls

Testing

1. Create or update a template/layout through the admin interface
2. Verify that the new custom post type is used for storing and retrieving templates/layouts

Related Issue

• Issue convert templates/layouts from static files to custom post type #13: convert templates/layouts from static files to custom post type

Notes

• This PR assumes that the wp-newsletter-builder plugin is properly set up and the required custom post type has been registered.
• Please make sure to thoroughly test the changes before merging, as this is a significant change to the template/layout handling system.

[attackant]

🐙