feat(machine): LNURL-withdraw executor for Bolt Card cash-out (LUD-03)

First, hardware-independent piece of Bolt Card tap-to-pay on the cash-out
flow. When a customer taps a Bolt Card, the ATM (which already has its
cash-out BOLT11) becomes the LNURL-*withdrawing* party: GET the card's
lnurlw voucher → GET callback?k1=…&pr=<invoice> so the card's wallet pays
the invoice. Settlement is still observed via the existing invoice watcher
(a returned ok=true means "card accepted the pull", not "cash dispensed").

- electron/lnurl-withdraw.ts: executeLnurlWithdraw() + lnurlwToHttps().
  Runs in the main process (Node fetch) to avoid renderer CORS, since LNURL
  endpoints send no CORS headers. Fully injectable fetch for testing.
- electron/lnurl-withdraw.test.ts: 12 tests (scheme mapping, two-step happy
  path passing k1+pr, ERROR surfacing, non-withdraw tag, amount-over-limit
  short-circuit, callback decline, network failure).
- IPC `lnurl:withdraw` (main) + preload + electron.d.ts.

Next: pcscd + an nfc-pcsc reader driver (reads the NTAG424 NDEF lnurlw),
then wire the tap into the cashOut displayingInvoice state + "tap or scan" UI.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/machine/electron/main.ts

@@ -42,6 +42,7 @@ import {
   type StoredBunkerBinding,
 } from './state-store.js'
 import { initializeHal, type HalInstance } from './hal-service.js'
+import { executeLnurlWithdraw } from './lnurl-withdraw.js'
 
 // ESM equivalent of __dirname
 const __filename = fileURLToPath(import.meta.url)
@@ -415,6 +416,20 @@ ipcMain.handle('app:recover', (): void => {
   reloadRenderer()
 })
 
+// Bolt Card cash-out: pull payment for the current invoice from a tapped card
+// via LNURL-withdraw. Runs in the main process (Node fetch) to dodge renderer
+// CORS. Returns once the card accepts; settlement arrives via the invoice
+// watcher. See lnurl-withdraw.ts.
+ipcMain.handle(
+  'lnurl:withdraw',
+  async (
+    _event,
+    args: { lnurlw: string; bolt11: string; amountMsat?: number }
+  ): Promise<{ ok: boolean; reason?: string }> => {
+    return executeLnurlWithdraw(args.lnurlw, args.bolt11, { amountMsat: args.amountMsat })
+  }
+)
+
 // State persistence IPC handlers
 ipcMain.handle('state:load-cassettes', () => loadCassettes())
 ipcMain.handle('state:set-cassettes', (_event, cassettes) => setCassettes(cassettes))