feat(scheduler): dispatch event on job failure, notify admins via notifications module

Add ?ModuleEventDispatcher to SchedulerRunService (fail-open, nullable).
Dispatch scheduler.job_failed event when a job fails with payload:
job_id, job_key, label, error_code, error_message, trigger_type.

New SchedulerJobFailedNotificationListener in notifications module
creates in-app admin notifications for users with JOBS_MANAGE
permission, scoped per tenant, with 30-min dedup per job_key.

Also fixes audit module manifest: system_audit_purge job_key was
mismatched (audit_system_purge vs system_audit_purge in DB).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

modules/audit/module.php

@@ -123,7 +123,7 @@ return [
 
     'scheduler_jobs' => [
         [
-            'job_key' => 'audit_system_purge',
+            'job_key' => 'system_audit_purge',
             'handler' => \MintyPHP\Module\Audit\Handler\SystemAuditPurgeJobHandler::class,
             'label' => 'System audit log cleanup',
             'description' => 'Purges system audit log entries older than the configured retention period',