briefcase's top-level .gitignore ignores node_modules, so I never noticed that
it was missing from my boilerplate .gitignore. I don't *really* need to add it
to that .gitignore, but if I want to cleanly eject directories from this
monorepo, it makes sense to keep the .gitignore files local to each project.
After deploying the version of this application that built everything in the
browser, which originally was the impetus for the entire project, I learned that
the babel in-browser transformer won't work. I'm not sure why, but I need to
move on from this project and do other work.
I ported the code to my boilerplate/typescript, which works. Wahoo!