Platform orders index: add clear subscription lock link

tests/Feature/AdminPlatformOrderIndexClearSubscriptionFilterLinkTest.php

@@ -0,0 +1,63 @@
+<?php
+
+namespace Tests\Feature;
+
+use App\Models\Merchant;
+use App\Models\Plan;
+use App\Models\SiteSubscription;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Tests\TestCase;
+
+class AdminPlatformOrderIndexClearSubscriptionFilterLinkTest extends TestCase
+{
+    use RefreshDatabase;
+
+    protected function loginAsPlatformAdmin(): void
+    {
+        $this->seed();
+
+        $this->post('/admin/login', [
+            'email' => 'platform.admin@demo.local',
+            'password' => 'Platform@123456',
+        ])->assertRedirect('/admin');
+    }
+
+    public function test_index_should_render_clear_subscription_filter_link_when_site_subscription_id_present(): void
+    {
+        $this->loginAsPlatformAdmin();
+
+        $merchant = Merchant::query()->firstOrFail();
+        $plan = Plan::query()->create([
+            'code' => 'po_clear_sub_filter_plan',
+            'name' => '平台订单清除订阅锁定测试套餐',
+            'billing_cycle' => 'monthly',
+            'price' => 10,
+            'list_price' => 10,
+            'status' => 'active',
+            'sort' => 10,
+            'published_at' => now(),
+        ]);
+
+        $sub = SiteSubscription::query()->create([
+            'merchant_id' => $merchant->id,
+            'plan_id' => $plan->id,
+            'status' => 'activated',
+            'source' => 'manual',
+            'subscription_no' => 'SS_CLEAR_SUB_FILTER_0001',
+            'plan_name' => $plan->name,
+            'billing_cycle' => $plan->billing_cycle,
+            'period_months' => 1,
+            'amount' => 10,
+            'starts_at' => now()->subDay(),
+            'ends_at' => now()->addMonth(),
+            'activated_at' => now()->subDay(),
+        ]);
+
+        $res = $this->get('/admin/platform-orders?site_subscription_id=' . $sub->id . '&keyword=abc');
+        $res->assertOk();
+
+        // 清除订阅锁定：应移除 site_subscription_id，但保留 keyword。
+        $res->assertSee('取消锁定订阅', false);
+        $res->assertSee('href="/admin/platform-orders?keyword=abc"', false);
+    }
+}