Set up frontend build tools

Add tools for processing CSS and JavaScript code.

• Add frontend build tools. Need to be able to bundle JS and CSS (if we even need to preprocess CSS at all 🤔), run Jest, and run linters, like we do now with Yarn and Rollup.
• Update CI scripts as needed to work with updated tools.
• Set up lefthook to run tests pre-push (should probably be a separate MR)

Yarn 4.x and Vite are potentially the right choices for this. Consider how this tooling will affect moving to Vue 3, or if there's anything we can do at this time to move that work forward.

Not in scope yet, coming later:

• Add Vue tooling (#53 - closed) • Sarah German

Maybe helpful:

• https://maxieluan.xyz/posts/hugo-vite-tailwind-theme-development/
• https://github.com/DcBD/vite-hugo-plugin
• https://medium.com/gumgum-tech/faster-development-experience-with-vite-hugo-and-preact-c08cbcfce5fb