fix: 清理按钮移出嵌套表单，独立提交到正确路由

internal/web/ui/templates/devices.html

@@ -46,16 +46,16 @@
         <button type="submit" name="action" value="rollback" class="secondary" {{if .RollbackSummary}}onclick='return confirm("将回滚到上一版运行配置：{{.RollbackSummary}}")'{{end}}>回滚运行配置</button>
         <a class="btn secondary" href="{{.BatchConfigURL}}">下发设备分配</a>
         <a class="btn secondary" href="/devices">清空选择</a>
-        {{$allOffline := true}}{{range .SelectedDevices}}{{if .Online}}{{$allOffline = false}}{{end}}{{end}}
-        {{if $allOffline}}
-        <form method="post" action="/devices/cleanup-offline" style="display:inline" onsubmit="return confirm('确认清理选中的 ' + {{len .SelectedDevices}} + ' 台离线设备及其全部关联数据？此操作不可恢复。')">
-          {{range .SelectedDevices}}<input type="hidden" name="device_id" value="{{.DeviceID}}">{{end}}
-          <button type="submit" class="btn danger">清理选中离线设备</button>
-        </form>
-        {{end}}
       </div>
     </div>
     {{end}}
+    {{$allOffline := true}}{{range .SelectedDevices}}{{if .Online}}{{$allOffline = false}}{{end}}{{end}}
+    {{if and .SelectedDeviceIDs $allOffline}}
+    <form method="post" action="/devices/cleanup-offline" style="margin:8px 0" onsubmit="return confirm('确认清理选中的 ' + {{len .SelectedDevices}} + ' 台离线设备及其全部关联数据？此操作不可恢复。')">
+      {{range .SelectedDevices}}<input type="hidden" name="device_id" value="{{.DeviceID}}">{{end}}
+      <button type="submit" class="btn danger">清理选中离线设备</button>
+    </form>
+    {{end}}
 
     <div class="table-wrap">
       <table id="device-list">