chore: rename skill to github-delivery

[Wibias]

Summary

• rename the published skill identity from shipping-github to github-delivery
• update package, distribution artifacts, installer paths, metadata, documentation, workflow outputs, tests, fixtures, and visible publication markers repository-wide
• update repository links and metadata to the intended Wibias/github-delivery slug
• refresh immutable regression hashes for the intentional repository-wide identifier migration

Migration impact

This changes the installed skill directory, distribution artifact names, manifest identity, repository metadata, and visible [shipping-github] markers to github-delivery. Existing installations must be replaced or migrated to a github-delivery directory after release.

The GitHub repository itself still needs to be renamed from shipping-github to github-delivery in repository settings after this PR merges; repository renames cannot be represented inside a pull request.

Validation

A one-time PR bootstrap job performs the repository-wide rename, restores the normal CI workflow, removes its temporary helper workflow, runs npm run check, and commits only the final rename diff. Normal PR CI then reruns on the resulting head.