Fail runs when proof is unsuccessful

[EauDoon]

Summary

• return a failing run exit code when the proof reports ok: false
• persist the same failure in the run manifest for CLI and GUI callers
• add a focused regression for an unsuccessful proof

Tests

• npm test (17/17)
• git diff --check HEAD^ HEAD

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.