GenerateAccount, RestoreFromSeed, RestoreViewOnly with deterministic
view key derivation (sc_reduce32(Keccak256(spend_secret))), matching
C++ account_base::generate(). Encrypted persistence via Argon2id
(time=3, mem=64MB) + AES-256-GCM in go-store.
Adds cn_sc_reduce32 to the CGo bridge for scalar reduction mod l,
required to convert a hash output into a valid Ed25519 secret key.
Co-Authored-By: Charon <charon@lethean.io>
