feat: integrate with htmx

templates/admin/system/availability/modal_create.html.twig

@@ -0,0 +1,7 @@
+{% extends 'htmx_modal.html.twig' %}
+
+{% block title %}Zeitraum hinzufügen{% endblock %}
+
+{% block content %}
+    {% include 'admin/system/availability/_form.html.twig' %}
+{% endblock %}