Prevent caching of old JS files

Either disable cache headers entirely (the JS file is not too big) or use the 'chunkhash' functionality of webpack to force the use of new JS files when they are available

Start by locating the webpack configuration and the response handling for generated JS files. Compare the two proposed cache-busting approaches and verify the chosen behavior by checking that a new deployment causes clients to load the new JS files rather than cached old ones.

Written by the indexing model from the issue text.