Disable Gift Creation in the Customer Portal

🔍 Problem Statement
Publishers who no longer offer gifting can hide the gift option during plan selection and checkout, but customers can still create new gifts through the customer portal (Gifts > Add a gift).

💡 User Story
As a publisher, I want to disable gift creation across all entry points, including the customer portal, so that customers can’t create new gifts while still having access to their existing ones.

🎯 Definition of Done (DoD)
✔ Gift creation can be disabled in the customer portal (Gifts > Add a gift).
✔ Direct access to the gift creation flow is blocked when gift creation is disabled.
✔ Existing gifts, including recipient details and shipping addresses, stay accessible to customers.
✔ This change will impact UI, specifically the Gifts section of the customer portal and the gift creation flow.