ERC-8441: hybrid post-quantum stealth address scheme
Was merged (namnc). It defines ERC-5564 `schemeId` 3, whose payment secret combines an ML-KEM-768 encapsulation with a secp256k1 ECDH secret, so an adversary who later gains a quantum computer still cannot tell from the announcement log who was paid. Spending stays on secp256k1, and the deployed ERC-5564 announcer and ERC-6538 registry are used unchanged.