refactor: rename modules directory to nix

flake.nix

@@ -41,7 +41,7 @@
   outputs =
     inputs:
     inputs.flake-parts.lib.mkFlake { inherit inputs; } (
-      (inputs.import-tree ./modules)
+      (inputs.import-tree ./nix)
       // {
         systems = import inputs.systems;
       }