Migrate to Tailwind CSS v3

We’re currently using an older version of TailwindCSS, and it’s about time we move to Tailwind v3. This version comes with a bunch of improvements such as performance boosts, better developer experience, and some handy new utilities that make styling a lot cleaner and more flexible.

This migration will involve:

- Upgrading Tailwind and related dependencies to version 3

- Updating tailwind.config.js to follow the v3 structure

- Checking all existing class names in the codebase and updating anything that breaks

- Testing existing component styles to make sure everything still looks and works as expected

- Since v3 makes dark mode easier to manage, we could explore adding it as a feature too