Unlock content for users who already paid for it

As a reader, I want any article I've already paid for to be accessible whenever I return to it, so that I never have to pay twice for the same content.

<img width="1352" height="1240" alt="Image" src="https://github.com/user-attachments/assets/c45e3312-7d43-48de-8d19-8cc7265a4048" />