Pending deletes were lost across app restarts because
recoverPersistedPendingChanges() never reconstructed CKRecord.ID
objects from persisted record names. Additionally, incoming iCloud
records for deleted playlists were blindly applied, and orphaned
playlist items in CloudKit would recreate placeholder playlists.
- Rebuild pendingDeletes array from UserDefaults on recovery
- Guard applyRemoteRecord against records pending local deletion
- Skip deferred items whose parent playlist is pending deletion
- Queue all playlist item deletions when deleting a playlist
- Clean up placeholder playlists for pending-delete playlists
