Migrate to UnoCSS/TailwindCSS classes

[ferferga]

We're currently using Vuetify's CSS classes, but we should switch to UnoCSS classes (which are using the same preset as Tailwind, hence the issue name so it's a 1:1 replacement, but faster at building and fully CSS-standard).

This allows us:

• Include only the styles we use, reducing bundle size.
• Modernizes the codebase (lots of new frontend projects are using Tailwind, this makes us catch up to them)
• Improve customization (since lots of the util classes use CSS variables, we can switch to those).

Currently, UnoCSS is configured to work prefixed as uno-, so gettings started it's a matter of installing the recommended extensions in VSCode and typing uno- in the class attribute of elements.

Useful resources

• Tailwind documentation (almost everything that applies here also applies to our setup)
• UnoCSS interfactive docs