Implements createEntryInvoice, checkPaymentStatus, payWinner, refundEntry,
redeemCashuToken, and recoverOrphanedPayments. Uses nostr-tools for NWC
protocol (NIP-47) and @cashu/cashu-ts for ecash fallback payouts.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>