The Dockerfile now builds the React admin UI itself in a dedicated
ui-build stage (added in #240), so building it again in a separate CI
job and shipping the result via artifact was doing the same work twice
per release — and the in-Docker build silently won anyway.
Dropping the CI job leaves a single UI build path and keeps
'docker build .' reproducible outside of CI.
master-ci / master-pr-ci keep their build-reactapp job: those are
compile-only checks that gate frontend errors on PRs and never produce
an artifact. release-xxx keeps its job too, since its zip release
artifact comes from 'dotnet publish' and never goes through Docker.
agile.zhou