fix(machine): wire up LNURL-withdraw completion callback

The onPaymentSuccess callback was passed to createATMServices but never
used, causing LNURL-withdraw claims to go undetected. Store the callback
so startLnurlCompletionPolling can trigger it when a withdrawal completes.

Refs: #24

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

lamassu-next/apps/machine/src/services/lightning.ts

@@ -791,8 +791,11 @@ function createATMServices(
   lightningPub: LightningPubClient,
   clink: CLINKClient,
   _identity: MachineIdentity,
-  _onPaymentSuccess: (preimage: string) => void
+  onPaymentSuccess: (preimage: string) => void
 ): ATMServices {
+  // Store callback for LNURL-withdraw polling to use
+  const onPaymentCallback = onPaymentSuccess
+
   return {
     /**
      * Generate an ndebit URI for cash-in