fix(nixos/sddm): use the kde sddm package

[isabelroses]

This resolves the error where the theme doesn't work if plasma6 isn't enabled. by default the packge is qt5 sddm, but catppuccin/sddm uses qt6.

[isabelroses]

closes #229

[getchoo]

i think this would be better as an assertion...but i'm not really sure how to reliably do that as sddm doesn't directly report its qt's major version

my first thoughts are asserting that pkgs.kdePackages.qtbase is in the buildInputs of config.services.displayManager.sddm.package or making a conditionally applied assertion for services.displayManager.sddm.package via a new option

[isabelroses]

I think the easiest thing would be to check what package is being used since it's either the qt5 one or the kde package.

[isabelroses]

or perhaps lib.mkDefault would be better so we don't get clashes with users that apply the plasma 6 desktop.

[getchoo]

I think the easiest thing would be to check what package is being used since it's either the qt5 one or the kde package.

that's what i meant with a conditional assertion. it wouldn't account for overriden packages ofc, but if someone really knows what they're doing they can disable it with an option

or perhaps lib.mkDefault would be better

i don't think it would as users could easily set the qt5 package as normal with no warning. assertions on the other hand provide a built in explanation of why we need to use the qt6 version when this happens

so we don't get clashes with users that apply the plasma 6 desktop

why would this happen?

[isabelroses]

why would this happen?

The duplicate package deceleration I mean.

[getchoo]

thanks!