moved common out of systems

common/global/nh.nix

@@ -0,0 +1,10 @@
+{
+  programs.nh = {
+    enable = true;
+    clean = {
+      enable = true;
+      dates = "weekly";
+      extraArgs = "--keep-since 7d --keep 3";
+    };
+  };
+}