flake: fix nix-hardware input and add flake-parts

flake.nix

···
 
     home-manager.url = "github:nix-community/home-manager";
 
-    nix-hardware = {
-      url = "github:nixos/nixos-hardware";
-      inputs.nixpkgs.follows = "nixpkgs";
-    };
+    nix-hardware.url = "github:nixos/nixos-hardware";
+
+    flake-parts.url = "github:hercules-ci/flake-parts";
 
     catppuccin.url = "github:catppuccin/nix";
   };