fix(machine): detect LNURL-withdraw completion from spent status

The polling was checking for `data.used > 0` but the LNURL endpoint
returns `{ status: 'ERROR', reason: 'Withdraw link is spent.' }` when
the link has been claimed. Check for this error response instead.

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

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

@@ -280,8 +280,12 @@ function startLnurlCompletionPolling(
 
       const data = await response.json()
 
-      // Check if the link has been used
+      // The LNURL endpoint returns:
-      if (data.link?.used > 0 || data.used > 0) {
+      // - { tag: 'withdrawRequest', ... } when link is still available
+      // - { status: 'ERROR', reason: 'Withdraw link is spent.' } when claimed
+      const isSpent = data.status === 'ERROR' && data.reason?.includes('spent')
+
+      if (isSpent) {
         console.log('[LNURL Poll] Withdrawal claimed!', uniqueHash)
         clearInterval(pollInterval)
 
@@ -294,6 +298,7 @@ function startLnurlCompletionPolling(
         // Use a placeholder preimage since LNURL-withdraw doesn't provide one directly
         onComplete(`lnurl-withdraw-${uniqueHash}`)
       }
+      // Note: Don't log on every poll - it can cause EPIPE errors in Electron
     } catch (e) {
       console.warn('[LNURL Poll] Error checking status:', e)
     }