Automatic design inheritance for custom product pages

New custom product pages now automatically inherit the structure, styles, and elements of the default product page when they are created. The generated pages remain completely independent and can be edited without affecting the original product page. A single custom product page can be assigned to multiple products, while the option remains hidden in the sales funnels to maintain a streamlined experience. This inheritance works as a one-time copy and does not synchronize with future changes to the default product page.