feat(skill): add skill for updating org with PF release/prerelease

[kmcfaul]

Closes #17

Added a skill to assist in org repo updates for PF releases & prereleases. Designed to be run inside the org repo to properly find scripts and package files.

The skill will:

• Use versions provided by the user, or fetch latest versions using org's internal script if none are provided.
• Update the site, framework, and root packages with the updated versions.
• Update the versions.json object array properly
• Provide the user with steps to regenerate screenshots for the release update.

I had attempted to get the skill to automatically run the build and screenshots, but ran into complications with cursor's sandbox permissions & build process timeouts, and didn't want to elevate any permissions so I changed it to only provide the user with directions.

[jpuzz0]

Since this is a release management skill — I think it'd be a better fit in pf-workflow (added in #15) rather than pf-react.