ci: add HOL skill-publish validate workflow

[internet-dot]

I opened this as a small validate-only check for the skill metadata in the repo.

A couple of repo-specific details I checked first:

• The community hub for Cursor — plugins, MCP servers, events, jobs, and thousands of developers building together

This adds one workflow for . and leaves the runtime code alone.
It only runs the schema and trust checks for the skill metadata in validate mode.

If you would rather place the workflow under a different filename or point it at a different skill directory, I can adjust the branch.

[vercel]

@internet-dot is attempting to deploy a commit to the Anysphere Team on Vercel.

A member of the Team first needs to authorize it.