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/Schedule.php

@@ -0,0 +1,28 @@
+<?php
+
+namespace App;
+
+use Symfony\Component\Scheduler\Attribute\AsSchedule;
+use Symfony\Component\Scheduler\Schedule as SymfonySchedule;
+use Symfony\Component\Scheduler\ScheduleProviderInterface;
+use Symfony\Contracts\Cache\CacheInterface;
+
+#[AsSchedule]
+class Schedule implements ScheduleProviderInterface
+{
+    public function __construct(
+        private CacheInterface $cache,
+    ) {
+    }
+
+    public function getSchedule(): SymfonySchedule
+    {
+        return (new SymfonySchedule())
+            ->stateful($this->cache) // ensure missed tasks are executed
+            ->processOnlyLastMissedRun(true) // ensure only last missed task is run
+
+            // add your own tasks here
+            // see https://symfony.com/doc/current/scheduler.html#attaching-recurring-messages-to-a-schedule
+        ;
+    }
+}