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>

composer.json

@@ -27,6 +27,7 @@
         "symfony/property-info": "7.4.*",
         "symfony/rate-limiter": "7.4.*",
         "symfony/runtime": "7.4.*",
+        "symfony/scheduler": "7.4.*",
         "symfony/security-bundle": "7.4.*",
         "symfony/serializer": "7.4.*",
         "symfony/twig-bundle": "7.4.*",