Consider moving styles to components library

[hobbes7878]

The team is now Svelte-ified across everything, including SREPs, so is there any reason why component styles should live separate from the components themselves?

This would gut a lot of the eisbaer theme lib, but also means those styles should be more straightforward for the team to maintain with the Svelte components.

Slight downsides:

1. Styles for components will be scoped, so overriding them (we do this.... irregularly, I think?) would mean fighting a little more with hierarchy in, say, a global.scss file in the kit.
2. Components that use SCSS variables (mostly to define font-sizes) won't be override-able. Alternatively, we could use CSS variables for those values, and maybe we should standardise around a root CSS variable style. (Which .... way future ... may open up the door to allowing dynamic injection of style overrides in components.)

[hobbes7878]

Point to the positive on 2: Bootstrap is also starting to roll out wider use of CSS variables for exactly this kind of thing. I think we're OK to start using it. https://getbootstrap.com/docs/5.0/customize/css-variables/