Upgrade to Tailwind 4

[zakini]

https://tailwindcss.com/docs/upgrade-guide

[zakini]

eslint-plugin-tailwindcss doesn't support v4 yet. Can't merge #37 until that's resolved, or if we swap to the official prettier plugin(s)

See francoismassart/eslint-plugin-tailwindcss#381 and francoismassart/eslint-plugin-tailwindcss#325

[zakini]

Recent work on this plugin: hyoban/eslint-plugin-tailwindcss#3 (comment)

[zakini]

Alternative plugin: https://github.com/schoero/eslint-plugin-better-tailwindcss