Move to importmaps, I guess

[ChaelCodes]

Rails/webpacker is retired, but it is receiving security updates and patches. Honestly, this app does nothing special with the frontend - just imports Bulma and moves on. We should just update to the new default - import maps. There shouldn't be any noticeable difference in what we deliver.

https://github.com/rails/webpacker

• [ ] Research what the transition looks like and what the steps are
• [ ] Test deploys - manual deploys of this branch to Render
• [ ] Test the dockerfile - Don't forget to run docker compose up --build