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 theirs. Trial-decrypt of 1000 notes is ~80ms in the browser; with fuzzy message detection on the roadmap, that drops to <10ms.