Release v2.0.0 contract hardening

[renezander030]

Summary

• add stable agent identities and nested delegation provenance
• add pre-admission validation records for schema, payload, semantic, policy, and authorization checks
• bind approvals to the exact review snapshot and complete arguments shown to the approver
• enforce requester, agent, actor, and signing-key separation of duties
• add durable terminal resolution receipts with independent delivery state
• revalidate approver, policy, workspace, and dispatcher authority immediately before dispatch
• add complete audit export manifests with count, sequence, event-set digest, and terminal hash
• add language-neutral RFC 8785 byte and digest vectors
• add adversarial review, identity, metadata, redaction, and lifecycle vectors
• update the importable n8n reference workflow and all release examples for v2

Validation

• python -m json.tool over every schema, example, and test corpus JSON file
• python scripts/generate_examples.py with byte-for-byte deterministic output
• python scripts/validate_contracts.py
• python -m unittest discover -s tests -v
• python -m compileall -q scripts tests
• git diff --check

Review notes

This is a major release because complete envelopes and several lifecycle records gain required fields. Stored v1 records remain valid against the immutable v1.0.0 schemas and should not be rewritten in place.

Publication is intentionally deferred until this PR has been reviewed and merged.