fix(canvas): 修复画布视频设置浮层遮挡和交互问题

- 将视频设置浮层改为挂载到页面根层级并使用自建浮层交互
- 避免被节点悬浮工具栏遮挡或点击面板内容时意外关闭
- 在画布配置节点组件中为视频设置浮层添加 placement 属性
- 更新文档描述以反映浮层交互方式的改进

web/src/app/(user)/canvas/components/canvas-config-node-panel.tsx

@@ -121,7 +121,7 @@ export function CanvasConfigNodePanel({ node, isRunning, inputSummary, inputs, o
             <div className={`mb-2 grid min-w-0 cursor-default items-center gap-2 ${mode === "text" ? "grid-cols-1" : "grid-cols-[minmax(0,1fr)_148px]"}`} onMouseDown={(event) => event.stopPropagation()}>
                 <ModelPicker className="canvas-compact-control h-10" config={config} value={config.model} onChange={(model) => onConfigChange(node.id, { model })} onMissingConfig={() => openConfigDialog(true)} fullWidth />
                 {mode === "video" ? (
-                    <CanvasVideoSettingsPopover config={config} buttonClassName="canvas-compact-control !h-10 !w-full !justify-start !rounded-lg !px-2" onConfigChange={(key, value) => onConfigChange(node.id, key === "videoSeconds" ? { seconds: value } : { [key]: value })} />
+                    <CanvasVideoSettingsPopover config={config} placement="topRight" buttonClassName="canvas-compact-control !h-10 !w-full !justify-start !rounded-lg !px-2" onConfigChange={(key, value) => onConfigChange(node.id, key === "videoSeconds" ? { seconds: value } : { [key]: value })} />
                 ) : mode === "image" ? (
                     <CanvasImageSettingsPopover config={config} placement="topRight" autoAdjustOverflow={false} buttonClassName="canvas-compact-control !h-10 !w-full !justify-start !rounded-lg !px-2" onConfigChange={(key, value) => onConfigChange(node.id, key === "count" ? { count: Number(value) || 1 } : { [key]: value })} />
                 ) : null}