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>

config/reference.php

@@ -468,7 +468,7 @@ use Symfony\Component\Config\Loader\ParamConfigurator as Param;
  *         }>,
  *     },
  *     scheduler?: bool|array{ // Scheduler configuration
- *         enabled?: bool|Param, // Default: false
+ *         enabled?: bool|Param, // Default: true
  *     },
  *     disallow_search_engine_index?: bool|Param, // Enabled by default when debug is enabled. // Default: true
  *     http_client?: bool|array{ // HTTP Client configuration