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/ScheduledJobRepository.php

@@ -240,6 +240,22 @@ class ScheduledJobRepository implements ScheduledJobRepositoryInterface
         return $updated !== false;
     }
 
+    public function deleteOrphanedJobs(array $validKeys): int
+    {
+        $validKeys = array_filter(array_map('trim', $validKeys), static fn (string $k): bool => $k !== '');
+        if ($validKeys === []) {
+            return 0;
+        }
+
+        $placeholders = implode(',', array_fill(0, count($validKeys), '?'));
+        $affected = DB::update(
+            "DELETE FROM scheduled_jobs WHERE job_key NOT IN ({$placeholders})",
+            ...array_map('strval', $validKeys)
+        );
+
+        return (int) $affected;
+    }
+
     private function normalizeRow(mixed $row): ?array
     {
         if (!is_array($row)) {