refactor(scheduler): use the recipe's default stateful schedule

Consolidate onto the symfony/scheduler recipe's App\Schedule (stateful +
processOnlyLastMissedRun, so missed runs after downtime still execute)
instead of a separate provider. Add the every-1-minute
ExpireAppointmentsMessage there, point scheduler_default at
schedule://default, and drop the redundant ExpireAppointmentsSchedule.
debug:scheduler shows the trigger registered.

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

config/packages/messenger.yaml

@@ -12,7 +12,7 @@ framework:
             failed: 'doctrine://default?queue_name=failed'
             sync: 'sync://'
             scheduler_default:
-                dsn: 'schedule://appointment_expiry'
+                dsn: 'schedule://default'
 
         routing:
             'App\Shared\Message\SendSmsMessage': async