Phase 10: Procurement-grade trust signals

- SECURITY_POSTURE.md: Threat model, controls, limitations (evidence-based)
- API_VERSIONING.md: Semver policy, backward compatibility rules, deprecation
- tools/audit_verify.py: CLI tool for audit packet integrity verification
- AUDIT_VERIFICATION.md: Verification tool usage and best practices
- BUYER_EVALUATION_CHECKLIST.md: Operational evaluation guide

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Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: 2 people