cava: init with rainbow theme

[brckd]

This PR inits the cava target which doesn't apply any changes by default yet. However, it adds a stylix.targets.cava.rainbow.enable option for a rainbow gradient, which is often used with this application.

Before	After

I'm not sure how and whether to handle gradients with stylix, but I used the colors for images from the style guide and sorted them rainbow-ishly. If there are more applications using gradients like this, it would make sense to add a stylix wide option to define the preferred gradient or solid color.

[trueNAHO]

I'm not sure how and whether to handle gradients with stylix, but I used the colors for images from the style guide and sorted them rainbow-ishly. If there are more applications using gradients like this, it would make sense to add a stylix wide option to define the preferred gradient or solid color.

IIRC, this is the first module with explicit gradient support.

[brckd]

I currently can't test this because of NixOS/nixpkgs#356817, but the suggested solution should work!

[trueNAHO]

fix in unstable now, no issue for me anymore

-- NixOS/nixpkgs#356817 (comment)

[brckd]

I was able to confirm that your suggested change works!

[trueNAHO]

Tested-by: NAHO <90870942+trueNAHO@users.noreply.github.com>

[brckd]

Thanks for the suggestions! I've successfully tested the changes after replacing the faulty references to cava with cfg.

[stylix-automation]

Successfully created backport PR for release-24.11:

• [release-24.11] cava: init with rainbow theme #731