配置化：同步失败原因TOPN与展示截断长度

app/Http/Controllers/Admin/PlatformOrderController.php

@@ -178,12 +178,15 @@ class PlatformOrderController extends Controller
 
         // 同步失败原因聚合（Top 5）：用于运营快速判断“常见失败原因”
         // 注意：这里用 JSON_EXTRACT 做 group by，MySQL 会返回带引号的 JSON 字符串，展示时做一次 trim 处理。
+        $topN = (int) config('saasshop.platform_orders.sync_failed_reason_top_n', 5);
+        $topN = max(1, min(20, $topN));
+
         $failedReasonRows = (clone $baseQuery)
             ->whereRaw("JSON_EXTRACT(meta, '$.subscription_activation_error.message') IS NOT NULL")
             ->selectRaw("JSON_EXTRACT(meta, '$.subscription_activation_error.message') as reason, count(*) as cnt")
             ->groupBy('reason')
             ->orderByDesc('cnt')
-            ->limit(5)
+            ->limit($topN)
             ->get();
 
         $failedReasonStats = $failedReasonRows->map(function ($row) {