feat(appointment): auto-expire unpaid bookings via Symfony Scheduler

Run the 15-min payment-expiry every minute through Symfony Scheduler so
unpaid pending bookings flip to expired without a system crontab. Install
symfony/scheduler; extract the expiry logic into AppointmentExpiryService
(reused by the existing command); add ExpireAppointmentsMessage + handler
and an #[AsSchedule] provider (RecurringMessage::every 1 minute); wire a
scheduler_default transport in messenger.yaml. Slots already free
just-in-time via isSlotTaken, so this only syncs the DB status.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/Appointment/Schedule/ExpireAppointmentsSchedule.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace App\Appointment\Schedule;
+
+use App\Appointment\Message\ExpireAppointmentsMessage;
+use Symfony\Component\Scheduler\Attribute\AsSchedule;
+use Symfony\Component\Scheduler\RecurringMessage;
+use Symfony\Component\Scheduler\Schedule;
+use Symfony\Component\Scheduler\ScheduleProviderInterface;
+
+#[AsSchedule('appointment_expiry')]
+final class ExpireAppointmentsSchedule implements ScheduleProviderInterface
+{
+    public function getSchedule(): Schedule
+    {
+        return (new Schedule())->add(
+            RecurringMessage::every('1 minute', new ExpireAppointmentsMessage())
+        );
+    }
+}