The build pipeline in CI should use the same docker files as desk builds

[dannystaple]

At the desk, I recommend using docker compose, which in turn uses the serve.Dockerfile.

Currently the at the desk dockerfile, and the CI setup node job can diverge on the version of node, and the content of node modules - not ideal.

This should be being built as a tool, and used to build the site.

Ideally in the workflow:

• The tool should be built with docker caching using the repo. Node modules should be in that build.
• Find a way to arrange mount points so node modules comes from the container, but the content does not both for at the desk compose and build.

This is likely to require changes to the compose file, and the ci on call build site workflow.