Fix assets in the demo app

[lcreid]

The demo app was not working the way it should have: It was not actually using any local assets, and was just using stock Bootstrap from CDN. This meant we weren't able to try things like customizing Bootstrap in the demo app. It also wasn't properly including our local application.scss file.

It turned out to be a long adventure to fix this, which ended up including:

• Regenerating the binstubs for all gems in the demo app. This didn't change anything as far as I can tell, but it shouldn't hurt to have these up-to-date.
• Making many config and initialization files match (as closely as possible) the files from a freshly generated Rails 7 app, generated with rails new --skip-hotwire -d sqlite --edge -j esbuild -c bootstrap .. Again, this didn't seem to make much difference, but it's not a bad thing to have them more up-to-date.
• Explicitly running the Rails server with bundle exec rails -s -b 0.0.0.0. I don't understand why the Rails in the bin directory wasn't doing this, but that's what fixed the problem of the assets not being processed.