fix(docker): restore npm to non_root builder image (#28519)

The non_root builder stage installs `nodejs` but not `npm`. Without `npm`
on PATH, prisma-python falls back to downloading a Node runtime via
nodeenv from nodejs.org, and that downloaded binary fails to load
`libatomic.so.1` — breaking `prisma generate` and the image build.

`npm` was dropped from this apk list in ca52e346b0. Restoring it lets
prisma-python use the system Node + npm, matching docker/Dockerfile
which already installs `npm` for the same reason.

docker/Dockerfile.non_root

@@ -24,7 +24,8 @@ RUN for i in 1 2 3; do \
         curl \
         openssl \
         libsndfile \
-        nodejs && break || sleep 5; \
+        nodejs \
+        npm && break || sleep 5; \
     done
 
 ENV UV_PROJECT_ENVIRONMENT=/app/.venv \