feat: add a booking event history for admins

Admins get /admin/history: one line per booking created, rescheduled or
released, per series created or ended, and per resource deleted with its
bookings. Sortable by time, kind, resource, booked day and both people;
filterable by period, kinds, who acted and resource type.

Events are snapshots written inside the same transaction as the change,
so a rolled-back booking leaves none and a released booking stays
readable. app:booking-events:prune keeps twelve months and needs a cron
entry on the server.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

templates/dashboard/index.html.twig

@@ -87,6 +87,17 @@
                     Buchbare Ressourcen und ihre Standorte verwalten.
                 </p>
             </a>
+
+            <a href="{{ path('app_admin_booking_event') }}"
+               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:history', { class: 'h-6 w-6 shrink-0 text-primary' }) }}
+                    <span class="text-lg font-bold">Ereignishistorie</span>
+                </div>
+                <p class="text-sm text-gray-500 pb-4">
+                    Nachvollziehen, wer welche Buchung angelegt, geändert oder freigegeben hat.
+                </p>
+            </a>
         {% endif %}
     </div>
 {% endblock %}