feat: put the access codes behind a feature flag

templates/dashboard/index.html.twig

@@ -49,14 +49,17 @@
             <p class="text-sm text-gray-500 pb-4">Alle Buchungen verwalten.</p>
         </a>
 
-        <a href="{{ path('app_access_code') }}"
-           class="group flex flex-col rounded-md border border-gray-200 p-6 hover:border-primary hover:bg-gray-50">
-            <div class="flex items-center gap-3 pb-2">
-                {{ ux_icon('lucide:key-round', { class: 'h-6 w-6 shrink-0 text-primary' }) }}
-                <span class="text-lg font-bold">Zugangscodes</span>
-            </div>
-            <p class="text-sm text-gray-500 pb-4">Codes für Türen, Aufzug und Schranke.</p>
-        </a>
+        {# The route 404s while the feature is off, so the card has to go with it. #}
+        {% if feature('access_codes') %}
+            <a href="{{ path('app_access_code') }}"
+               class="group flex flex-col rounded-md border border-gray-200 p-6 hover:border-primary hover:bg-gray-50">
+                <div class="flex items-center gap-3 pb-2">
+                    {{ ux_icon('lucide:key-round', { class: 'h-6 w-6 shrink-0 text-primary' }) }}
+                    <span class="text-lg font-bold">Zugangscodes</span>
+                </div>
+                <p class="text-sm text-gray-500 pb-4">Codes für Türen, Aufzug und Schranke.</p>
+            </a>
+        {% endif %}
 
         {#
             The header is deliberately not navigation, so the dashboard is the only place an