feat(admin): 刷新改为独立的圆形图标按钮（42px），主操作按钮单独一行

- 12 个后台页的刷新统一为 .refresh-btn，固定在页头最右，悬停旋转
- 渠道管理「添加渠道」、并发分组「新增分组」移到页头下方单独一行
- 渠道空状态文案同步

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frontend/src/views/LogsView.vue

@@ -157,7 +157,7 @@ const sourcePill = (s) => ({
   <section class="space-y-4">
     <div class="page-head">
       <h2 class="page-title">日志管理</h2>
-      <button @click="load" class="btn-soft"><Icon name="refresh" class="w-3.5 h-3.5" /> 刷新</button>
+      <button @click="load" class="refresh-btn" title="刷新" aria-label="刷新"><Icon name="refresh" :size="18" /></button>
     </div>
     <!-- KPI strip — dense pills aligned with the dashboard tints -->
     <div class="grid grid-cols-2 md:grid-cols-4 gap-3">