[BUG REPORT] S3: 文件服务器元数据可以引用已删除的块 - 通过 readDeleted=true 进行掩蔽,在扫除后会导致数据丢失

### Describe the bug
An S3 object's filer entry can point at a chunk that has been deleted (tombstoned) in the volume index. Because the filer read path unconditionally appends `readDeleted=true`, the object stays fully readable (HEAD/GET 200 with the original size and Last-Modified), so the inconsistency is invisible to clients. Once the volume is vacuumed, the tombstoned needle is physically reclaimed and the object suddenly returns 404 — silent, delayed data loss.