chore(ui): 统一后台按钮样式 + 清理少量 inline margin

resources/views/admin/plans/index.blade.php

@@ -125,7 +125,7 @@
         <form method="post" action="/admin/plans/seed-defaults" onsubmit="return confirm('仅在当前没有任何套餐时才会初始化。确认执行吗？');">
             @csrf
             <button type="submit" class="btn">一键初始化默认套餐（空库）</button>
-            <div class="muted muted-xs" style="margin-top:6px;">安全护栏：当库中已存在套餐时会自动阻止，避免污染运营数据。</div>
+            <div class="muted muted-xs mt-6">安全护栏：当库中已存在套餐时会自动阻止，避免污染运营数据。</div>
         </form>
     </div>
 </div>

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

@@ -17,7 +17,7 @@
             </div>
 
             @if((string) ($defaults['order_type'] ?? '') === 'renewal')
-                <div class="muted muted-xs" style="margin-top:6px;">
+                <div class="muted muted-xs mt-6">
                     提示：该订单类型为「续费」。在订单完成「标记支付并生效 → 同步订阅」后，将会对该订阅执行续期/延长到期时间（以系统同步结果为准）。
                 </div>
             @endif

resources/views/admin/site_subscriptions/index.blade.php

@@ -206,7 +206,7 @@
         @endphp
         <a class="btn" href="{!! $createOrderFromSubIndexUrl !!}">创建续费订单（带当前筛选）</a>
     </div>
-    <div class="muted muted-xs" style="margin-top:6px;">用于运营从订阅目录快速补单/续费：会把当前 merchant_id/plan_id/site_subscription_id 作为默认值带到下单页。</div>
+    <div class="muted muted-xs mt-6">用于运营从订阅目录快速补单/续费：会把当前 merchant_id/plan_id/site_subscription_id 作为默认值带到下单页。</div>
 </div>
 
 <div class="card">