rubygems/release-gem@v1 runs `bundle exec rake release` to invoke the
push. The migration commit removed that task. Restored, trimmed to just
`gem push <gem_file>` since the workflow already built + smoke-checked
the artifact in earlier steps. If invoked locally without a built gem,
falls back to build + smoke-check + push so the local path matches CI.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>