Payment Receipt Route

FREE, no-auth: a BIP-340-signed payment receipt for one verdict-governed EIP-3009 payment (services/payment_receipt.py).

Body: {event: the signed /review verdict, args: the payment args it bound, tx_hash?: the settlement tx, resource_url?, max_verdict_age_seconds?, terms_hash?, authorization_signature?: the payer's EIP-3009 signature (verified against the bound fields and the token's on-chain EIP-712 domain), output_hash?: sha256 of the delivered result}. Returns the nine fields an agent needs before retrying: endpoint, network, asset, max_amount, payer, facilitator_verdict, settlement_id, denial_reason, retry_state (paid_do_not_retry | pending | denied_do_not_retry | expired_do_not_retry | not_paid_safe_to_retry), plus idempotency_key (the EIP-3009 nonce = the verdict's decision_ref). retry_state is read from the token's authorizationState(payer, nonce) on chain, so it holds even without a tx_hash. settlement_id is set only when /verify-execution proves the tx is the payment the verdict bound. 422 (unsigned) when the verdict does not verify or does not bind these args.