feat(scheduler): delete orphaned jobs and block editing of unregistered jobs

Adds deleteOrphanedJobs() to clean up stale job_keys during ensureSystemJobs, and prevents editing jobs that are no longer registered in the runtime registry.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/Repository/Scheduler/ScheduledJobRepositoryInterface.php

@@ -28,4 +28,7 @@ interface ScheduledJobRepositoryInterface
         ?string $errorCode,
         ?string $errorMessage
     ): bool;
+
+    /** Delete jobs whose job_key is not in the given list of valid keys. Returns affected row count. */
+    public function deleteOrphanedJobs(array $validKeys): int;
 }