receipts

Per-transaction inbound NIGHT receipts (#284), classified by UTXO-set provenance in the indexer subscription: a genuine receipt is a transaction that created NIGHT to us without spending any of our UTXOs. Our own sends (which return change to us) are NEVER receipts, so a consumer wiring this to a notification will never tell the user they "received" their own change. Each event carries the exact amount received IN THAT transaction — not a balance delta. Cold by default (emptyFlow) when no subscription is wired (e.g. tests).