darkman integration

[MoetaYuko]

fixes #447, much easier than I expected thanks to existing infra

needs #459 which introduced geoclue as a hard dependency of gammastep

users can edit .config/darkman/config.yaml to disable auto transition

[MoetaYuko]

@end-4 any comments on this feature? feel free to close if not worth adding.

[end-4]

ugh... i'm hesitant to add this since there's already blue light filter and one can always change the brightness if needed

if we add this feature i think i can just give the dark mode toggle an "Auto" mode and make a new user option in case someone wants to enable/disable it by default without digging in hyprland config
thank you for your work

[MoetaYuko]

darkman has two major advantages:

1. retrieve geolocation-based transition time from geoclue (like gammastep does)
2. run custom user scripts. e.g., I have additional scripts to switch gtk/qt/kvantum themes between light/dark variants

anyway, whoever needs this can cherry-pick in their fork.

[clsty]

I actually kinda like this PR... @end-4 maybe reconsider this one? That autorun-theme-changing-custom-script feature sounds great. Of course it's your decision.