fix: warn if country code missing

apps/web/app/admin/cities/new/page.tsx

@@ -573,6 +573,11 @@ function ConfirmStep({
             className="block w-full rounded-md border border-gray-300 px-3 py-2 text-sm focus:border-brand-500 focus:outline-none focus:ring-1 focus:ring-brand-500"
             placeholder="DE"
           />
+          {!countryCode && (
+            <p className="mt-1 text-xs text-amber-600">
+              No transit scoring without a country code.
+            </p>
+          )}
         </div>
 
         <div className="bg-gray-50 rounded-md p-3">