Backend modules cannot move out of cli while they import cli-internal
paths. @n8n/backend-services is the package for the backend services
that many modules share. It sits above @n8n/db and below n8n. This
commit adds the empty package with its build, lint and test setup. The
next commits move the shared services into it one area at a time.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
