React Update

[Jason Siefken]

Hi everyone! The build system for the React frontend has been switched from (the now deprecated) react-scripts to vite.

There are a couple of consequences:
   * pretext-react now must be loaded with a `<script type="module" ...>` tag. This means that current projects using the react frontend need to be recompiled with the latest Pretext (Rob just made the modification yesterday).
   * Development is much easier! When running in "hot reload mode" via `npm run start`, you can now navigate to any subfolder to see the react frontend in action. For example, you may make a symbolic link to your compiled pretext (as long as it was compiled with the debug.react.local flag) in to the pretext-react development directory, and you can then navigate to that directory and see everything live :-).

Now that `overhaul` is fully integrated, hopefully we can get serious about integrating pretext-react with all the Runestone features; maybe by the end of the summer it can be the new default!