Clean up dev and release CLJS and JS builds (#30072)

There are now four families of FE builds:

- `build` does a one-shot dev build.
- `build-watch` watches for changes and does dev rebuilds; no server.
- `build-hot` is `build-watch` plus a development web server.
- `build-release` is a one-shot release mode build.

Each family has `:cljs` and `:js` variants, to build just one part.