* WFM, force dark mode in windows11

[evolighting]

What I do:
1. add config, `decorations-theme-variant`, add windows attributes for it
2. search `preferred_theme` at windows impl, make it change according to `decorations-theme-variant`

config lile:

[window]
decorations-theme-variant = "Dark"

WFM, test like:

[evolighting]

build with this patch in rioterm 0.2.31, works on windows 11

[raphamorim]

Hey @evolighting thanks for the issue, I assume it works for other OS too, like macos right. at least at a quick glance of the pr