prefill property
FR-25 — an optional prefill (from WalletSendEntry.push, via GoRouter
extra). null = the organic empty form. Seeds the (screen-owned) form
controllers in initState; lockRecipient opens the recipient read-only.
A prefill is NOT pre-confirmed — the same validate → review → authorize
path and the same gating run as an organic send.
Implementation
final WalletSendRequest? prefill;