fix(payment): align plate-follow cash preview with wallet balance

Use cash wallet for plate follow cashiers and stop stubbing methods when Gateway is missing.

inc/helpers/aksrt-pay.php

@@ -86,9 +86,8 @@ if (!function_exists('aksrt_list_cash_payment_methods')) {
             : ['alipay', 'wechatpay', 'paypal', 'stripe'];
 
         if (!class_exists('\AKSRT\Payment\Gateway')) {
-            return $logged_in
-                ? [['id' => 'balance', 'name' => __('站内余额', 'aksrt')]]
-                : [['id' => 'alipay', 'name' => __('支付宝', 'aksrt')]];
+            // No gateway manager → no real methods (avoid dead balance/alipay stubs).
+            return [];
         }
 
         $methods = [];