fix(ns): class_exists() must use FQCN after PSR-4

Bare class_exists('Balance') looks up global Balance, always false
under AKSRT\* namespaces → REST 403 on balance exchange and friends.
Rewrite string checks to AKSRT\{Domain}\{Class}.

src/AKSRT/Payment/OrderRepositoryAdmin.php

@@ -63,10 +63,10 @@ trait OrderRepositoryAdmin {
         }
 
         $resolved_order_numbers = array_keys($orders);
-        $shipping_map = class_exists('Shipping')
+        $shipping_map = class_exists('AKSRT\\Payment\\Shipping')
             ? Shipping::get_instance()->get_summary_map($resolved_order_numbers)
             : [];
-        $after_sale_map = class_exists('AfterSale')
+        $after_sale_map = class_exists('AKSRT\\Payment\\AfterSale')
             ? AfterSale::get_instance()->get_summary_map($resolved_order_numbers)
             : [];
 
@@ -509,7 +509,7 @@ trait OrderRepositoryAdmin {
             'summary' => [
                 'order_number' => (string) ($order['order_number'] ?? ''),
                 'status' => $status,
-                'status_label' => class_exists('Order') ? (Order::get_valid_statuses()[$status] ?? $status) : $status,
+                'status_label' => class_exists('AKSRT\\Payment\\Order') ? (Order::get_valid_statuses()[$status] ?? $status) : $status,
                 'amount' => $amount,
                 'currency_symbol' => '¥',
                 'created_at' => (string) ($order['created_at'] ?? ''),