The CI host builds with the legacy Docker builder (buildx/BuildKit missing on
the runner). Drop the '# syntax' directive and the 'RUN --mount=type=cache'
npm cache mount from the Dockerfile, and remove DOCKER_BUILDKIT=1 from the
workflow. Restores a green build so registry.alwisp.com/jason/mrp-qrcode:latest
publishes and PORT can roll the container off the pinned old digest.
The legacy builder ignores '# syntax=docker/dockerfile:1.7' and fails at the
first 'RUN --mount=type=cache' in the deps stage, which is why runs #193, #382
and #433 all died in ~3s at Step 5/38. Activating dockerd's integrated BuildKit
backend fixes the build so :latest publishes again.
- drop per-commit :sha tag (registry stays one tag per repo)
- remove the built image and prune dangling layers after push so CI builds
stop accumulating orphan images on the Unraid host