[rafagil11]

Summary

• Update circom-to-soroban-hex to parse and validate the curve field from verification key JSON inputs, ensuring we only serialize BLS12-381 keys.
• Add a proper BLS12-381 verification key (packages/zk/build/verification_key.json) to the repository so the tool has a valid input for on-chain contract configurations.

Root Cause

Previously, circom-to-soroban-hex ignored the curve property in verification key JSON files. Since the only pre-existing vkey (packages/circuits/build/verification_key.json) was BN254 (bn128), running the tool silently marshaled a BN254 curve into a BLS12-381 byte layout, creating a mis-curved key blob that would later fail cryptographic checks on Soroban.

Technical Changes

1. Updated VerificationKeyJson struct in packages/contracts/circom-to-soroban-hex/src/main.rs to include a curve: String field.
2. Added validation inside vk_hex to verify that curve == "bls12381". If any other curve (such as bn128) is encountered, the tool panics with a clear mismatch error message naming the required curve.
3. Committed the actual BLS12-381 verification key at packages/zk/build/verification_key.json as specified.

Verification / Tests

• Running circom-to-soroban-hex vk packages/circuits/build/verification_key.json now aborts with a curve mismatch error.
• Running circom-to-soroban-hex vk packages/zk/build/verification_key.json successfully emits the expected BLS12-381 hex blob.

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Closes #65