feat(工具栏设置): 添加工具栏配置页面及功能实现

实现工具栏配置页面，允许用户调整工具栏按钮的顺序和可见性
包含主工具栏、画布控制和尾部按钮三个区域的配置
支持恢复默认布局功能

Ink Canvas/MainWindow.xaml.cs

@@ -100,6 +100,14 @@ namespace Ink_Canvas
             */
             InitializeComponent();
 
+            BoardBorderToolsPopup.CustomPopupPlacementCallback =
+                (popupSize, targetSize, offset) => new[]
+                {
+                    new CustomPopupPlacement(
+                        new Point((targetSize.Width - popupSize.Width) / 2, -popupSize.Height - 5),
+                        PopupPrimaryAxis.Vertical)
+                };
+
             BlackboardLeftSide.Visibility = Visibility.Collapsed;
             BlackboardCenterSide.Visibility = Visibility.Collapsed;
             BlackboardRightSide.Visibility = Visibility.Collapsed;