meta: Move stylix-background to separate package

Long-term this won't be necessary once backgrounds become optional in
stylix.

modules/desktop.nix

@@ -9,7 +9,6 @@
 let
   inherit (lib.types) float int;
   inherit (config.modules.system) username;
-  inherit (config.lib.stylix.colors.withHashtag) base00;
   inherit (nix-config.packages.${pkgs.system}) aleo-fonts;
   inherit (builtins) attrValues;
 
@@ -34,22 +33,10 @@ let
     noto-fonts-cjk-sans
     maple-mono
     noto-fonts-emoji
-    stdenvNoCC
-    imagemagick
     ;
 
-  stylix-background = stdenvNoCC.mkDerivation {
+  stylix-background = pkgs.callPackage ../packages/stylix-background.nix {
-    pname = "stylix-background";
+    color = config.lib.stylix.colors.base00;
-    version = base00;
-
-    dontUnpack = true;
-
-    nativeBuildInputs = [ imagemagick ];
-
-    postInstall = ''
-      mkdir -p $out
-      magick -size 1x1 xc:${base00} $out/wallpaper.png
-    '';
   };
 
   cfg = config.modules.desktop;

packages/stylix-background.nix

@@ -0,0 +1,19 @@
+{
+  stdenvNoCC,
+  imagemagick,
+  color ? "181818",
+}:
+
+stdenvNoCC.mkDerivation {
+  pname = "stylix-background";
+  version = "1.0.0-${color}";
+
+  dontUnpack = true;
+
+  nativeBuildInputs = [ imagemagick ];
+
+  postInstall = ''
+    mkdir -p $out
+    magick -size 1x1 xc:#${color} $out/wallpaper.png
+  '';
+}