feat: enable entering additional remarks in offer confirmation

templates/groups/booking/_offer_accept_confirmation_modal.html.twig

@@ -4,7 +4,8 @@
 
 {% block content %}
     {% from '_partials/_validation_errors.html.twig' import validation_alert %}
-    {{ validation_alert(confirmationForm, 'Bitte akzeptiere die AGB, um die Buchung abzuschließen.', false) }}
+    {# Generic title: both fields can fail, and each renders its own message inline. #}
+    {{ validation_alert(confirmationForm, null, false) }}
 
     <p class="mb-6">
         Möchtest du dieses Angebot jetzt verbindlich buchen?
@@ -17,6 +18,7 @@
             'hx-swap': 'outerHTML',
         }
     }) }}
+        {{ form_row(confirmationForm.remarks) }}
         {{ form_row(confirmationForm.termsAccepted) }}
 
         <div class="mt-6 flex flex-col space-y-4 md:flex-row md:space-y-0 justify-between">