feat: move to single-user config

modules/flake-parts.nix

@@ -15,7 +15,7 @@
     _: machine:
     inputs.nixpkgs.lib.nixosSystem {
       specialArgs = { inherit inputs; };
-      modules = [ (machine.buildFunction machine) ];
+      modules = [ (config.repo.helpers.mkHost machine) ];
     }
   ) config.repo.machines;