refactor(frontend): swap WindiCSS out for UnoCSS

[ravenclaw900]

Part 1.75 out of 3 to cleanup frontend

WindiCSS's last commit was on June 30, and UnoCSS is by the same author and supports the same things, while being faster and more feature-rich. It also lets us use icons in CSS, and looks like it will eventually let us use themes for #29. It supports a svelte-scoped mode, which uses Svelte's native CSS class scoping, so that the global stylesheet doesn't grow with the addition of every single-use class.

[MichaIng]

Great cleanup for (our) code indeed. Adds a lot of (build) dependencies, but I guess it has no or only minor impact on the size of compiled frontend assets, right?

[ravenclaw900]

I guess it has no or only minor impact on the size of compiled frontend assets

The compiled frontend assets are actually slightly smaller in size, but there's not much difference.

[MichaIng]

I thought so: compiling might take longer, but no negative effect on results 👍.

[ravenclaw900]

Interestingly, compiling should actually be shorter, as shown by the benchmarks in https://antfu.me/posts/reimagine-atomic-css#performance. Really the only caveat of switching to UnoCSS is that there are still a couple of bugs that need to be worked around (like unocss/unocss#2379).