Card: point at the second digest attestation, and document mirroring

Repack without macOS AppleDouble files: the previous archive extracted 101 files on Linux and failed its own checksum

Dataset card, generated by bench/build_hf_card.py

CandidBench world: post-canary archive, matches world_digest.json

Add dataset card; disable auto viewer (single-archive dataset)

Publish DataBench world archive (gold-free, 48 files)

initial commit