feat: expose contradicted requirements in jev_decide

[xujiantop-crypto]

Summary

• add recommendation.contradicted_requirements to jev_decide results
• report zero-based requirement indexes already identified by contradictsRecommendation()
• preserve the existing selected, status, and human-readable warning behavior
• document the response field and cover valid, invalid, contradicted, and non-contradicted recommendations

This addresses the structural part of #43 without adding escalate_on_contradiction or changing the default recommendation policy. That behavior can remain a separate maintainer decision.

Testing

• node --test --test-name-pattern=jev_decide test/mock.test.mjs (5 passed)
• npm test (240 passed)
• npm run typecheck
• npm run build

[jkudish]

Thank you for this — the structural field was the right idea. It's now part of #46 (merged), which supersedes this PR. Closing in favor of that change.