Add package.nix and cleanup build process

flake.nix

@@ -1,7 +1,7 @@
 {
   description = "kutu wm environment";
 
-  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-26.05";
 
   outputs = { self, nixpkgs }:
   let
@@ -12,17 +12,22 @@
   in {
     devShells.${system}.default = pkgs.mkShell {
       packages = with pkgs; [
-        ruby
+        (ruby.withPackages (ps: [
+          ps.ffi
+        ]))
         gcc
         pkg-config
 
         xorg.libxcb
         xorg.xcbutilwm
+        xorg.xrandr
+        xorg.xprop
       ];
 
       shellHook = ''
         echo "kutu dev shell"
       '';
     };
+    packages.${system}.default = pkgs.callPackage ./package.nix {};
   };
 }