refactor: enable firewall explicitely for 'hecuba' host

hosts/hecuba/default.nix

@@ -44,6 +44,10 @@
 
   security.sudo.wheelNeedsPassword = false;
 
+  networking = {
+    firewall.enable = true;
+  };
+
   services.openssh = {
     enable = true;
     harden = true;