refactored theme configuration to use stylix instead of individually theming each program

modules/sys/environment/sddm.nix

@@ -0,0 +1,12 @@
+{
+  pkgs,
+  self,
+  config,
+  ...
+}: {
+  services.displayManager.sddm = {
+    enable = true;
+    wayland.enable = true;
+    package = pkgs.kdePackages.sddm;
+  };
+}