Add moving major branch publishing

[bcomnes]

Summary

• add opt-in goversion publish -major-branch
• derive and publish the moving vN GitHub Actions branch after all other release stages succeed
• protect updates with force-with-lease and support dry-run, reuse, resume, and configured remotes
• expose library metadata and CLI status output
• document the workflow and add unit plus bare-remote integration coverage

Validation

• go test ./...
• go vet ./...
• git diff --check

Follow-up

After this is released, go-bump can update its pinned goversion dependency and self-host releases with major-branch: true.