go to nh for auto

cleaning

nixos/programs/nh.nix

@@ -4,6 +4,8 @@
   # Cleanup stays on nix.gc (see system/nix.nix) to avoid two GC timers.
   programs.nh = {
     enable = true;
+    clean.enable = true;
+    clean.extraArgs = "--keep-since 4d --keep 3";
     flake = "/home/prouk/flake";
   };
 }