Recover shard.00543.mds (lost during original chunk_1 upload)

Fix chunk_001/index.json: drop missing shard.00543.mds (lost in original upload)

Restructure train/: nest shards into chunk subdirs (batch 97/98)

Restructure train/: nest shards into chunk subdirs (batch 10/98)

Restructure train/: nest shards into chunk subdirs (batch 9/98)

Restructure train/: nest shards into chunk subdirs (batch 8/98)

Restructure train/: nest shards into chunk subdirs (batch 7/98)

Restructure train/: nest shards into chunk subdirs (batch 6/98)

Restructure train/: nest shards into chunk subdirs (batch 5/98)