refactor(machines) rename tower -> nova

flakes/nixos.nix

@@ -104,7 +104,7 @@ in {
         ];
     };
 
-    tower = mkNixos {
+    nova = mkNixos {
       modules =
         defaultModules
         ++ [
@@ -112,7 +112,7 @@ in {
             home-manager.users.michael = import ../user/environments/nixos-server/home.nix;
           }
 
-          ../machines/tower/configuration.nix
+          ../machines/nova/configuration.nix
         ];
     };
   };