feat: Add(+enhance) color/theme usage specification

[bigpick]

Info

Right now, the palette at https://github.com/pineapplegiant/spaceduck#colors-palette- just has a "SYN ID" column, that sort of says where a color should be used, but is pretty limited.

What would be really great is if we had a full (or at least, much more detailed) spec that outlined what colors should be used for what and where. Granted, it's hard to specify exactly all possible fields since each port will likely use slightly different variations for names and whatnot, but having a solid basis to work off would be a huge improvement.

E.g, Dracula has https://spec.draculatheme.com/# which is nice because its a lot more specific for things like syntaxes, which would help when filling out a port for something like VS code or Atom Syntax or w.e.

Nord has https://www.nordtheme.com/docs/colors-and-palettes which is a looser guide (not specific syntax names) and more of a "when to use what where" spec.

Personally, I think having a combination of both would make it so that the ports have a much better chance at all being consistent, and your original vibe of the theme is persisted across them all.

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I think the first step though is getting the colors/palette finalized first, though.

1. Finalize colors/palette
2. Define/create/publish spec
3. Update existing ports to match/comply, use a guide for future ports (updating when necessary)