docs: make decision entity labels optional

[abrichr]

Summary

• make the attended-decision entity class optional presentation metadata
• explain that no separate qualification-author role is required
• use the neutral record or item fallback when no class is set
• preserve Standard and Regulated qualification requirements for safety contracts

Validation

• uv run mkdocs build --strict
• python scripts/validate_docs.py
• uv run pytest tests/test_validate_docs.py -q
• git diff --check