Add Skills support for easy install

[bahadirarslan]

I think it will be better to add npx skills support to easy install option for everyone.

[VladimirBrejcha]

This is aligned with the registry direction. We plan to support an easy install command, likely via an npm/npx CLI, but first we are adding registry validation, lock-file support, and a dry-run sync/doctor flow so install does not silently copy stale skills. I’ll keep this issue as the public installer/bootstrapper tracking item.