feat: generate draft assignments from a staffing matrix

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

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