Wallet contract / ETH-implicit accounts (NEP-518, NEP-641)

[r-near]

Background. NEP-518 introduces Ethereum-style implicit accounts (0x…) backed by an auto-deployed wallet contract. NEP-641 (still an unapproved NEP) defines off-chain message signing for wallet contracts.

Current behavior. 0x… accounts render as opaque strings with no type awareness. There's no wallet-contract message-signing path, though the app's existing message-discriminant infrastructure for NEP-413 / NEP-366 can be extended.

Work.

• (unblocked) Recognize 0x + 40-hex receiver IDs as Ethereum-style implicit accounts and label them in the UI for signer context.
• (blocked on NEP-641 approval) Implement wallet-contract message signing: parse the NEP-641 payload and extend the message-discriminant scheme once the spec is finalized.

Acceptance. 0x… accounts are detected and labeled; NEP-641 signing is implemented after the NEP is approved (tracked, not started until then). Keep the two parts independently shippable.