ERC-8373 Binds Post-Quantum Keys On-Chain, Cutoff Enforced

Post-quantum key binding launched. Scheme binds classical→PQ keys on-chain, not appends. Cutoff enforces PQ companion post-anchor; back-catalog stays valid. ML-DSA-65 and SLH-DSA-SHA2-192s live, dual-family. Recovery layer unproven: operator-attested, ZK deferred. Claims recompute, not quantum-proof.