feat(billing): 平台订单创建页展示订阅关联提示并加测试

resources/views/admin/platform_orders/form.blade.php

@@ -7,6 +7,16 @@
 <div class="card mb-20">
     <p class="muted muted-tight">用于总台运营手工创建一笔平台订单（演示/补单/线下收款录入）。</p>
     <p class="muted">创建后可在「平台订单」列表中继续推进：标记支付并生效 → 同步订阅（形成最小收费闭环）。</p>
+
+    @if(($siteSubscription ?? null) && $siteSubscription->id)
+        <div class="mt-10">
+            <div class="muted">本订单将关联订阅：</div>
+            <div>
+                <a class="link" href="/admin/site-subscriptions/{{ $siteSubscription->id }}">{{ $siteSubscription->subscription_no }}</a>
+                <span class="muted">（订阅ID：{{ $siteSubscription->id }}）</span>
+            </div>
+        </div>
+    @endif
 </div>
 
 <form method="post" action="/admin/platform-orders" class="card form-grid">