docs: describe qualified entity labels for decisions

[abrichr]

Summary

• describe the domain-neutral V2 qualified entity label for attended decisions
• document explicit V2 negotiation and the V1 record / item fallback
• state that actual identity values remain on the customer-controlled runner

Release dependency

This is documentation for the coordinated Types, Flow, Desktop, and Cloud V2
release. Do not merge or deploy it before the V2 producer, consumers, and
capability negotiation are released together.

Validation

• uv run mkdocs build --strict

[abrichr]

Superseded by #102, which is merged and deployed. #102 documents the released Types and Cloud support, the pending Flow and Desktop authoring path, the neutral fallback, and recertification in one canonical page.