refactor(工具栏): 将BorderTools从Border改为Popup控件并优化显示逻辑

重构工具栏中的BorderTools控件，将其从Border改为Popup控件，并添加自定义位置回调
优化显示/隐藏逻辑，使用IsOpen属性替代Visibility控制
更新相关动画效果调用为对应的Popup版本
调整UI样式和布局，提升视觉一致性

Ink Canvas/MainWindow.xaml.cs

@@ -108,10 +108,17 @@ namespace Ink_Canvas
                         PopupPrimaryAxis.Vertical)
                 };
 
+            BorderTools.CustomPopupPlacementCallback =
+                (popupSize, targetSize, offset) => new[]
+                {
+                    new CustomPopupPlacement(
+                        new Point(targetSize.Width / 2 - popupSize.Width / 2, -popupSize.Height),
+                        PopupPrimaryAxis.Vertical)
+                };
             BlackboardLeftSide.Visibility = Visibility.Collapsed;
             BlackboardCenterSide.Visibility = Visibility.Collapsed;
             BlackboardRightSide.Visibility = Visibility.Collapsed;
-            BorderTools.Visibility = Visibility.Collapsed;
+            BorderTools.IsOpen = false;
             LeftSidePanelForPPTNavigation.Visibility = Visibility.Collapsed;
             RightSidePanelForPPTNavigation.Visibility = Visibility.Collapsed;
             TwoFingerGestureBorder.Visibility = Visibility.Collapsed;