Detect OS Dark/Light Mode?

### Description

Hi!

I love that colorls supports and comes with themes for dark/light modes, if set by the user per-usage. I noticed an issue from some time ago #165, in which a commenter suggested using ANSI colors. The way I use my terminal mostly these days is with the integrated term in VSCode, which I've set to switch theme based on my daily OS (mac/windows) dark/light cycle. Unfortunately, I don't know how to auto set colorls to use the appropriate theme based on light/dark mode.

Would it possible to either bake-in such functionality to be configured as the user wishes, or does anyone have any easy scripts or aliases or something that can take of this?

The easiest option for me or anyone else really would be to support ANSI color names within the color.yaml files, and let the terminal themes take care of the rest

- Relevant Issues : #165 kinda
- Type of issue :
- [ ] Installation
- [ ] Font-related
- [x] Feature request
- [ ] Bug in existing feature
- [ ] Developer mode : Code quality / Tests / Documentation

Start by inspecting how color.yaml themes are loaded and review related issue #165. Clarify whether the goal is OS dark/light detection, user-configurable switching, or ANSI color names; done means one defined approach works in the supported terminal environments and is documented.

Written by the indexing model from the issue text.