Weekly garbage collection

hosts/server.nix

@@ -34,6 +34,17 @@ with lib.my;
     neovim
   ];
 
+  nix = {
+    settings = {
+      auto-optimise-store = true;
+    };
+    gc = {
+      automatic = true;
+      dates = "weekly";
+      options = "-d --delete-older-than 7d";
+    };
+  };
+
   modules.networking.tailscale = {
     enable = true;
     restrictSSH = false;