ops/nixos: run nix-collect-garbage daily, except on clients

ops/nixos/lib/client.nix

@@ -7,6 +7,8 @@ let
   inherit (lib) mkBefore;
 in
 {
+  nix.gc.automatic = false;
+
   users.users.lukegb.packages = mkBefore (with pkgs; [
     depot.nix.pkgs.copybara
     direnv

ops/nixos/lib/common.nix

@@ -82,4 +82,10 @@ in
   system.activationScripts.lukegb-hgrc = lib.stringAfter [ "users" "groups" ] ''
     ln -sfn ${./hgrc} /home/lukegb/.hgrc
   '';
+
+  # Clean up daily.
+  nix.gc = {
+    automatic = true;
+    dates = "*-*-* 05:00:00";
+  };
 }