Replaces the Jenkinsfile with a .gitea/workflows/build-push.yml that
builds on pushes to main and pushes `latest` + `sha-<short>` tags to the
Gitea package registry using the REGISTRY_URL variable and
REGISTRY_TOKEN secret. Adds a docker-compose.yml that pulls the
published image for deployment.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
