feat(platform-orders): 退款总额统计（详情页+导出）

tests/Feature/AdminPlatformOrderExportTest.php

@@ -125,6 +125,7 @@ class AdminPlatformOrderExportTest extends TestCase
         $this->assertStringContainsString('订阅ID', $content);
         $this->assertStringContainsString('最近批量生效时间', $content);
         $this->assertStringContainsString('最近批量生效管理员', $content);
+        $this->assertStringContainsString('退款总额', $content);
 
         // include_meta=1 时应包含 meta(JSON) 列
         $res2 = $this->get('/admin/platform-orders/export?include_meta=1');

tests/Feature/AdminPlatformOrderRefundReceiptTest.php

@@ -74,6 +74,13 @@ class AdminPlatformOrderRefundReceiptTest extends TestCase
 
         $this->assertSame('partially_refunded', $order->payment_status);
         $this->assertNotNull($order->refunded_at);
+
+        // 确保退款轨迹可用于对账统计
+        $totalRefunded = 0.0;
+        foreach ($refunds as $r) {
+            $totalRefunded += (float) (data_get($r, 'amount') ?? 0);
+        }
+        $this->assertSame(10.0, $totalRefunded);
     }
 
     public function test_platform_admin_can_add_refund_receipt_and_mark_fully_refunded_when_total_refund_reaches_paid_amount(): void