Adds a workflow that triggers on push to main: builds backend/frontend
Docker images, pushes to Gitea container registry, pulls and restarts
on the host, health checks, prunes old images, and sends ntfy notifications.
docker-compose.yaml updated to pull pre-built images from registry and
includes act_runner as a 4th service.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
