fix(zk): enforce address binding, verifier hardening, and structural guards (#348)

[s6pa1rta3n-lab]

Summary

Resolves #348 by hardening the ZK verification pipeline, enforcing address binding, and implementing structural guards across circuits, contracts, and the SDK:

1. Address-Binding & Verifier Hardening (ZK-072 / REPLAY matrix):

   • Implemented address-to-field canonical encoding via SHA256 reduction modulo $r$ for Stellar Address types (Account and Contract), matching circuit field expectations.
   • Enforced recipient address binding in Soroban contract withdraw entrypoint: contract verifies that recipient_field passed in public inputs strictly matches the hash of the caller's target address.
   • Updated circuit linear combination and contract verifier to validate all 8 public inputs (pool_id, root, nullifier_hash, recipient, amount, relayer, fee, denomination).

2. Structural & VK Verification Guards:

   • Enforced structural validation on Groth16 proofs (G1/G2 point uncompressed lengths, canonical formatting) and Verifying Keys (gamma_abc element length matching public input count + 1).
   • Validated schema versions deterministically derived from public input schemas.

3. SDK & Merkle Tree Alignments:

   • Updated ProofGenerator.prepareWitness and PublicInputs schemas to handle 8 inputs with canonical hex encoding.
   • Preserved zero-account semantics (fee == 0 implies zero relayer field) while validating address formatting.
   • Fixed manifest refresh script and schema parity test matrix.

Verification

• Noir Circuits: 124/124 tests pass (nargo test --workspace).
• Soroban Contracts: 96/96 tests pass (cargo test).
• SDK & E2E Suites: 57/57 test suites pass, 862/862 tests pass (npm test).

Payout Routing

• EVM (Base/Arbitrum/Polygon/ETH): 0xF46C9F6d70C50BF81ef3588AB523a90a594a2F89
• Stellar: GCL6OXAMLD75BMTINA6EMRUDWK5THQUSHMYNLSNBCJAPZJHNYJTUNIBC