Have better defaults on YAML files selected in the Playground

The behavior we'd like to see is that all interview files are selected on the Packages screen by default, but it remembers if you deliberately deselect any files. Has caused issues with newbies using the playground.

<img width="640" height="670" alt="Image" src="https://github.com/user-attachments/assets/c0676b17-6380-477b-aea8-8eafc4372e6f" />