Prove a zap invoice was paid and record the zap

Records the zap the ticket describes once its invoice is proven paid: a supplied preimage (sha256 must equal the invoice's payment hash) IS the proof; without one the server asks the recipient's provider via LUD-21 verify at the URL the ticket carries (202 while unpaid — poll at ~2.5 s). A provider without verify needs the preimage (PROOF_REQUIRED). Idempotent on the payment hash: a replay answers recorded: "already" with the image's live counters. An attested zap bumps the image's zap_count/zap_total_sats and notifies the recipient; an unattested one is recorded as a receipt only. No authentication — the signed ticket is the credential. Never gated by ZAPS_ENABLED. Rate limited 60/min/IP.