Improve error message when running e2e tests against the wrong build

It would be good if there was a helpful error message when running e2e tests again a build created with either `yarn start` or `yarn dist`. It should say something like "It looks like you did not create a test build. Rerun your build with either `yarn start` or `yarn dist`"

Start by locating the e2e test setup or entry point that detects builds created with yarn start or yarn dist. Reproduce the wrong-build case, then make the failure explain that a test build is required and rerun the build with either command; verify the e2e tests show the new message.

Written by the indexing model from the issue text.