act-based Gitea runner images do not ship Maven, so the publish job failed
with 'mvn: command not found'. Add the Maven Wrapper (Maven 3.9.11) and use
./mvnw. Fail early with a clear message when REGISTRY_TOKEN is not available.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01G71TQ5jDETVwdUJxGAwaiT
