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:

• Official repo for spec & SDK of MCP Apps protocol - standard for UIs embedded AI chatbots, served by MCP servers
• Build interactive UIs for MCP tools — charts, forms, dashboards — that render inline in Claude, ChatGPT and any other compliant chat client
• Excalidraw built with MCP Apps, running in Claude

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.