fix flake parts config

flake.nix

@@ -9,13 +9,16 @@
   };
   outputs = { flake-parts, nixpkgs, ... }@inputs: (
     flake-parts.lib.mkFlake { inherit inputs; } {
-      nixosConfigurations = {
+      flake.nixosConfigurations = {
         freun-dev = nixpkgs.lib.nixosSystem {
           system = "x86_64-linux";
           specialArgs = inputs;
           modules = [ ./hosts/freun-dev ];
         };
       };
+      systems = [
+        "x86_64-linux"
+      ];
     }
   );
 }