法币提现（WITHDRAW_FIAT）

{
  "orderType": "WITHDRAW_FIAT",
  "source": {
    "type": "INTERNAL_ACCOUNT",
    "details": { "currency": "USD" }
  },
  "destination": {
    "type": "BANK_ACCOUNT",
    "details": {
      "countryCode": "US",
      "currency": "USD",
      "accountNo": "1234567890",
      "accountName": "ACME INC",
      "bankName": "CHASE",
      "bankCode": "CHASUS33"
    }
  },
  "amount": { "value": "1000.00", "currency": "USD" },
  
  "partnerOrderId": "partner_order_fiat_wd_001",
  "callbackUrl": "https://merchant.example.com/callback/order"
}

{
  "success": true,
  "data": {
    "orderId": "ord_fiat_wd_20240101_001",
    "orderType": "WITHDRAW_FIAT",
    "status": "CREATED",
    "createdAt": "2024-01-01T10:00:00Z"
  }
}