A trade proof of ['proof','zap','<receiptId>'] is now checked by verifyZapReceipt
(kind-9735 signature + p = seller + decodable bolt11 amount + embedded 9734
request) and counted as paymentVerified, shown on TradeReputationCard as
'payment-verified (zap receipt)' - a real tier above the self-reported claim.
Honest ceiling: proves the seller's LNURL provider acknowledged a payment, not
that goods changed hands. NIP.md documents the zap proof variant.
