Use lockfile, yarn, --frozen-lockfile

Noticed a discussion on this in another thread.

It's best not to mix yarn and npm.  You should also use `--frozen-lockfile` or `--pure-lockfile` when installing into a docker image.  yarnpkg/yarn#4147

docker/client.Dockerfile

@@ -1,11 +1,12 @@
 FROM node
 
 COPY web/package.json /client/package.json
+COPY web/yarn.lock /client/yarn.lock
 WORKDIR /client
-RUN npm install
+RUN yarn install --frozen-lockfile
 COPY web /client
 RUN yarn run build --mode docker
 
 FROM nginx
 RUN rm -rf /usr/share/nginx/html/*
-COPY --from=0 /client/dist /usr/share/nginx/html
+COPY --from=0 /client/dist /usr/share/nginx/html