Eject from CRA, migrate to Vite 8

[rgov]

Create React App is deprecated and the JavaScript ecosystem has moved onto its 3,412,485th build tool, Vite 8. This resolves #82.

Warning

Slop, to be clear.

1. I first had Claude Code Opus 4.6 migrate on its own to Vite 8, with access to a Chrome DevTools MCP to check for console errors.
2. Once it had succeeded, I reviewed the set of changes and started over again making incremental steps towards that goal while keeping the build system under CRA as long as possible. Those steps are basically code cleanliness steps like being explicit about uses of JSX, and using ESM import statements instead of require().
3. Once the preparatory steps were complete, I had it migrate everything to Vite 7, based on esbuild.
4. Then I did the final step forward to Vite 8 with the new Rust-based compiler.

I did a cursory test pointing to the Alvin backend and hit a regression with moment-duration-format which was previously being loaded automagically but now needs to be explicit. Other functionality seemed fine (in play mode).

@figuernd I didn't know you were working on changes this week, sorry for the merge conflict. It should rebase easily onto this though.

[rgov]

I don't love these shims but I'm willing to live with them.

[figuernd]

Didn't Vite 8 come out TODAY? 😭

[rgov]

The HN post is 17 hours old, bro. We're already starting the transition from Rolldown/Vite to Yeetup/Spite. If we don't merge this we're going to have so much tech debt by next week.