feat(machine): production safety — disable mock fallback and ndebit

When VITE_ALLOW_MOCK_FALLBACK is unset (production default), the ATM
now shows a maintenance screen instead of silently falling back to mock
services when hardware or Lightning initialization fails. Also disables
ndebit/CLINK in production since the static ndebit pointer is replayable
— cash-in uses LNURL-withdraw only (single-use by design).

- Add allowMockFallback config field (Electron IPC + types)
- Add strict config validation (no localhost, require private key)
- Gate all catch-block fallbacks behind allowMockFallback
- Disable debit approval service and ndebit generation in production
- Add maintenance screen in App.vue when initError is set

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/machine/electron/main.ts

@@ -118,6 +118,7 @@ ipcMain.handle('get-config', () => {
     validatorDevice: process.env.VITE_LAMASSU_VALIDATOR_DEVICE,
     dispenserDevice: process.env.VITE_LAMASSU_DISPENSER_DEVICE,
     cassettes: process.env.VITE_LAMASSU_CASSETTES,
+    allowMockFallback: process.env.VITE_ALLOW_MOCK_FALLBACK === 'true',
   }
 })