Zera Wallet v3: ZKP core + real data layer

Wallet v3 has the Groth16 proving core wired in, plus a real data layer (no more localStorage mocks). Note scanning runs against the actual nullifier tree, wallet unlock derives keys from a passphrase via Argon2id. The bit that took the longest wasn't the proving — that's a wasm import — it was the note discovery . Every block, the wallet has to try-decrypt every commitment to see which ones are…