Oh yeah, I didn't catch that `bin/dev` calls the `Procfile` which in
turn calls `yarn build --watch`, which leaves out the important
`--public-path=/dev-assets` argument!
Calling `yarn dev` instead keeps us consistent!
We add jsbuilding-rails to get esbuild running in the app, and then we copy-paste the files we need from impress-2020 into here!
I stopped at the point where it was building successfully, but it's not running correctly: it's not sure about `process.env` in `next`, and I think the right next step is to delete the NextJS deps altogether and use React Router instead.
