Add agent false-pass gate proof

[yangfei222666-9]

Summary

• Add a local False-Pass Gate for AI-agent success claims
• Block unsupported done/readiness claims without passing evidence
• Require explicit cannot_claim boundaries
• Document reviewer path and proof index limitations

Validation

• python scripts/check_false_pass_gate.py --self-test examples/false_pass_gate/fixtures
• python -m pytest tests/test_false_pass_gate.py -q
• python -m json.tool docs/proof_index.json
• npm run typecheck

Cannot Claim

• Does not prove remote CI until GitHub Actions runs
• Does not prove production readiness
• Does not prove public adoption or recruiting validation