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:

• TaskFlow is a team task app that helps you manage work in one place. It supports shared tasks, live updates, login with tokens, and background notifications
• Each tool handles one job, such as login, live updates, storage, or messages
• Why does TaskFlow use so many tools?

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.