feat(platform-orders): 退款总额统计（详情页+导出）

app/Http/Controllers/Admin/PlatformOrderController.php

@@ -537,6 +537,7 @@ class PlatformOrderController extends Controller
                 '最近退款时间',
                 '最近退款金额',
                 '最近退款渠道',
+                '退款总额',
             ];
 
             if ($includeMeta) {
@@ -596,6 +597,13 @@ class PlatformOrderController extends Controller
                         (string) (data_get($latestRefund, 'refunded_at') ?? ''),
                         (float) (data_get($latestRefund, 'amount') ?? 0),
                         (string) (data_get($latestRefund, 'channel') ?? ''),
+                        (function () use ($refunds) {
+                            $total = 0.0;
+                            foreach ($refunds as $r) {
+                                $total += (float) (data_get($r, 'amount') ?? 0);
+                            }
+                            return $total;
+                        })(),
                     ];
 
                     if ($includeMeta) {