对账明细导出：增加 exported_at 摘要行

app/Http/Controllers/Admin/PlatformOrderController.php

@@ -436,9 +436,10 @@ class PlatformOrderController extends Controller
             // UTF-8 BOM，避免 Excel 打开中文乱码
             fwrite($out, "\xEF\xBB\xBF");
 
-            // 订单摘要（基础两行）
+            // 订单摘要（基础三行）
             fputcsv($out, ['order_id', (string) $order->id]);
             fputcsv($out, ['order_no', (string) $order->order_no]);
+            fputcsv($out, ['exported_at', now()->format('Y-m-d H:i:s')]);
 
             // 可选：导出更多订单快照字段（便于财务/对账留档，不必另截图）
             if ($includeOrderSnapshot) {

tests/Feature/AdminPlatformOrderExportLedgerTest.php

@@ -92,6 +92,10 @@ class AdminPlatformOrderExportLedgerTest extends TestCase
         $this->assertStringStartsWith("\xEF\xBB\xBF", $content);
         $this->assertStringStartsWith("\xEF\xBB\xBF", $content2);
 
+        // exported_at 摘要行
+        $this->assertStringContainsString('exported_at,', $content);
+        $this->assertStringContainsString('exported_at,', $content2);
+
         // 核心表头
         $this->assertStringContainsString('record_type,receipt_type,channel,amount,biz_time,created_at,admin_id,note', $content);
         $this->assertStringContainsString('record_type,receipt_type,channel,amount,biz_time,created_at,admin_id,note', $content2);