Add a theme that complies with WCAG AAA

Hi,

I’ve spent countless hours searching for the right theme, but I always come back to Modus (https://github.com/protesilaos/modus-themes). It strikes a great balance between clarity and aesthetics, and its WCAG AAA compliance makes it especially comfortable to use. Currently I am using “High Contrast Dark”

Would you be open to a PR to add the Modus theme? https://github.com/mountain-loop/yaak/tree/main/plugins/themes-yaak/src/themes

Thanks for Yaak.