[codex] Harden agent memory rights transitions

[8Dionysus]

Summary

• Require transition-scoped memory promotion rights to name allowed transitions for nomination and confirmation, not only promotion/demotion/rescue.
• Give reviewer and evaluator explicit transition scopes in their source profiles and regenerated agent registry.
• Align the memory posture doc and validator tests with the stricter contract.

Validation

• python scripts/validate_agents.py
• python -m pytest -q tests
• git diff --cached --check
• public-share secret-pattern scan over the diff returned no matches.