Add a reusable libswoc release skill (#11)

Publishing libswoc depends on a fragile manual handoff from the
reviewed ATS lib/swoc history. The existing procedure assumes one
maintainer's fork and leaves commit ordering and source comparison
ambiguous.

This patch adds a repository-local release skill that discovers
remotes, preserves ATS commit order and authorship, distinguishes
intentional tree differences, builds in the current ATS Fedora image,
and verifies branch and tag publication.

Co-authored-by: GPT-5 Codex