feat: manage stateVersion through hostHelper

hostHelper.nix

@@ -10,5 +10,15 @@ in
     modules = [
       {networking.hostName = hostname;}
       (./hosts/${hostname})
+
+      {
+        # This value determines the NixOS release from which the default
+        # settings for stateful data, like file locations and database versions
+        # on your system were taken. It‘s perfectly fine and recommended to leave
+        # this value at the release version of the first install of this system.
+        # Before changing this value read the documentation for this option
+        # (e.g. man configuration.nix or on https://nixos.org/nixos/options.html).
+        system.stateVersion = hostOptions.stateVersion; # Did you read the comment?
+      }
     ];
   }