chore(zk): add pinned Noir version compatibility gate for reproducibl…

[Litezy]

Closes #308

Summary

Adds a pinned Noir version compatibility gate for circuit builds to enforce deterministic ZK compilation. Introduces .noir-version as the source of truth and adds a validation script to fail fast on toolchain mismatches, ensuring consistent artifact generation across environments.

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Type of Change

• Bug fix
• New feature
• Smart contract change
• Documentation
• Breaking change
• Other (please describe)

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Checklist

• Tests added or updated
• No hardcoded secrets or private keys
• If contract change: cargo test passes
• If frontend change: npm run typecheck passes
• If backend change: npm test passes
• Related issues linked (Closes ZK-064)
• Self-review completed
• Code follows project style guidelines

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Screenshots (if applicable)

N/A

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Testing

• Verified .noir-version is correctly read by validation script
• Tested mismatch scenario to confirm CI/script fails as expected
• Confirmed nargo --version matches pinned version before build
• Successfully rebuilt circuits with enforced version gate
• Ensured CI pipeline runs version check before circuit compilation

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Additional Notes

• Introduces .noir-version as the single source of truth for Noir toolchain version
• Adds script-based enforcement for local and CI environments
• Prevents silent artifact drift caused by Noir upgrades
• Ensures reproducible circuit builds across contributors and CI
• Designed to fail fast when toolchain mismatch is detected

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