Prepare LegalScope public release materials

[EternWang]

Summary

Prepares LegalScope for a professional public release across GitHub and Hugging Face.

This PR:

• rewrites the root README for a clearer benchmark overview, counts, findings, quickstart, release boundary, citation, and disclaimer;
• expands the public data card, scoring rubric, release-status, and AI-workflow documentation;
• adds provenance, Hugging Face release guidance, a publication checklist, and contributing guidelines;
• keeps the public name as LegalScope and documents the metadata-only release boundary.

Privacy / Release Boundary

This PR does not add full workbooks, prompt matrices, reference answers, model-output matrices, human review sheets, non-de-identified judgments, paper draft files, provider logs, API keys, or private source documents.

Verification

• python -m pytest -q -> 2 passed
• Checked public package for historical internal naming and private file types before preparing this PR.