Close pre-sale registration a configurable time before events start.

Events gain nullable presale_closure_enabled / presale_close_minutes_before
overrides; null inherits the new site_settings defaults (enabled, 120 min).
A shared resolver computes the effective cutoff, which the public event API
exposes as presaleClosesAt and the public booking endpoint enforces. Door and
admin ticket creation are not gated.

Admin: toggle + duration picker in the event modal (pre-filled from the site
default) and a matching default card on Settings › General. Public: the event
page shows "Registration Closed" after the cutoff and the checkout page
redirects back.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

frontend/src/app/admin/settings/page.tsx

@@ -8,8 +8,10 @@ import { parseDate } from '@/lib/utils';
 import Card from '@/components/ui/Card';
 import Button from '@/components/ui/Button';
 import Input from '@/components/ui/Input';
+import DurationInput from '@/components/admin/DurationInput';
 import {
   Cog6ToothIcon,
+  TicketIcon,
   GlobeAltIcon,
   ClockIcon,
   EnvelopeIcon,
@@ -47,6 +49,8 @@ export default function AdminSettingsPage() {
     maintenanceMode: false,
     maintenanceMessage: null,
     maintenanceMessageEs: null,
+    presaleClosureEnabled: true,
+    presaleCloseMinutesBefore: 120,
   });
 
   const [legalSettings, setLegalSettings] = useState<LegalSettingsData>({
@@ -508,6 +512,69 @@ export default function AdminSettingsPage() {
             </div>
           </Card>
 
+          {/* Pre-sale Closure defaults */}
+          <Card>
+            <div className="p-6">
+              <div className="flex items-center gap-3 mb-6">
+                <div className="w-10 h-10 bg-green-100 rounded-full flex items-center justify-center">
+                  <TicketIcon className="w-5 h-5 text-green-600" />
+                </div>
+                <div>
+                  <h3 className="font-semibold text-lg">
+                    {locale === 'es' ? 'Cierre de Preventa' : 'Pre-sale Closure'}
+                  </h3>
+                  <p className="text-sm text-gray-500">
+                    {locale === 'es'
+                      ? 'Valor por defecto para los eventos. Cada evento puede cambiarlo en su ventana de edición.'
+                      : 'Default for events. Each event can override this in its edit dialog.'}
+                  </p>
+                </div>
+              </div>
+
+              <div className="flex items-center justify-between p-4 bg-gray-50 rounded-lg mb-4">
+                <div>
+                  <p className="font-medium">
+                    {locale === 'es' ? 'Cerrar la preventa antes del evento' : 'Close pre-sale before the event starts'}
+                  </p>
+                  <p className="text-sm text-gray-500">
+                    {settings.presaleClosureEnabled
+                      ? (locale === 'es' ? 'Las inscripciones en línea se cierran antes del inicio' : 'Online registration stops before the start time')
+                      : (locale === 'es' ? 'Las inscripciones siguen abiertas hasta el inicio' : 'Registration stays open until the event starts')}
+                  </p>
+                </div>
+                <button
+                  type="button"
+                  onClick={() => updateSetting('presaleClosureEnabled', !settings.presaleClosureEnabled)}
+                  className={`relative inline-flex h-6 w-11 items-center rounded-full transition-colors ${
+                    settings.presaleClosureEnabled ? 'bg-green-500' : 'bg-gray-300'
+                  }`}
+                >
+                  <span
+                    className={`inline-block h-4 w-4 transform rounded-full bg-white transition-transform ${
+                      settings.presaleClosureEnabled ? 'translate-x-6' : 'translate-x-1'
+                    }`}
+                  />
+                </button>
+              </div>
+
+              {settings.presaleClosureEnabled && (
+                <div className="max-w-md">
+                  <DurationInput
+                    label={locale === 'es' ? 'Cerrar la preventa este tiempo antes del inicio' : 'Close pre-sale this long before the start'}
+                    valueMinutes={settings.presaleCloseMinutesBefore}
+                    onChange={(minutes) => updateSetting('presaleCloseMinutesBefore', minutes)}
+                    unitLabels={locale === 'es'
+                      ? { minutes: 'minutos', hours: 'horas', days: 'días' }
+                      : { minutes: 'minutes', hours: 'hours', days: 'days' }}
+                    helper={locale === 'es'
+                      ? 'Se aplica a los eventos que no tienen su propia configuración.'
+                      : 'Applies to events that have not set their own value.'}
+                  />
+                </div>
+              )}
+            </div>
+          </Card>
+
           {/* Maintenance Mode */}
           <Card>
             <div className="p-6">