feat: complete Phase 2 shared contracts and corpus

[OgeonX-Ai]

Summary

• consume provenance-pinned cas-contracts v0.1.0 schemas with offline standard-library validation
• expand v0.2 golden and adversarial corpus with explicit capability coverage
• publish deterministic v0.2.0 benchmark release artifacts and cross-platform verification

Verification

• 21 unit tests passed
• golden v0.2: 8/8 passed
• adversarial v0.2: 6/6 passed
• release artifacts regenerate byte-identically
• PowerShell verification and git diff check passed

[chatgpt-codex-connector]

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