fix(UI): 优化弹出菜单位置和层级管理

修复弹出菜单在移动时位置不更新的问题，添加节流机制避免频繁刷新
使用Win32 API强制刷新弹出菜单位置并提升到最顶层
调整浮动工具栏和弹出菜单的样式和位置
移除未使用的字体样式定义

Ink Canvas/MainWindow.xaml.cs

@@ -112,9 +112,10 @@ namespace Ink_Canvas
                 (popupSize, targetSize, offset) => new[]
                 {
                     new CustomPopupPlacement(
-                        new Point(targetSize.Width / 2 - popupSize.Width / 2, -popupSize.Height),
+                        new Point(targetSize.Width / 2 - popupSize.Width / 2, -popupSize.Height - 8),
                         PopupPrimaryAxis.Vertical)
                 };
+
             BlackboardLeftSide.Visibility = Visibility.Collapsed;
             BlackboardCenterSide.Visibility = Visibility.Collapsed;
             BlackboardRightSide.Visibility = Visibility.Collapsed;