Improve Hugging Face dataset card

[jang1563]

Summary

• add Hugging Face viewer configs to the generated dataset card
• add provenance, intended-use, limitation, contact, and leaderboard Space references to the generated card
• document the viewer-config contract in the HF release/data-dictionary docs

Validation

• .venv/bin/ruff check scripts/export_hf_dataset.py tests/test_hf_export.py
• .venv/bin/python -m py_compile scripts/export_hf_dataset.py scripts/upload_hf_dataset.py
• .venv/bin/python scripts/export_hf_dataset.py --out-dir /tmp/labcraft_hf_full_card_check --release-name card_check_full --copy-plots
• .venv/bin/python scripts/validate_hf_export.py /tmp/labcraft_hf_full_card_check
• .venv/bin/python scripts/upload_hf_dataset.py /tmp/labcraft_hf_full_card_check --repo-id example/LabCraft-Eval
• .venv/bin/python -m pytest