[codex] Add premium docs and HF data dictionary

[jang1563]

Summary

• add architecture and trajectory walkthrough docs for human reviewers
• add an HF export data dictionary and link it from the README
• include a Data Fields section in the generated Hugging Face dataset card

Validation

• .venv/bin/ruff check .
• .venv/bin/python -m pytest tests/test_hf_export.py tests/test_hf_upload.py tests/test_inspect_task.py
• .venv/bin/python -m pytest
• .venv/bin/python scripts/export_hf_dataset.py --out-dir build/hf_export_docs_smoke --release-name docs_smoke --copy-plots
• .venv/bin/python scripts/validate_hf_export.py build/hf_export_docs_smoke
• .venv/bin/python scripts/upload_hf_dataset.py build/hf_export_docs_smoke --repo-id example/LabCraft-Eval