feat: 添加白板模式自动全屏功能

- 新增"白板模式自动全屏"设置选项
- 进入白板模式时自动全屏，退出时恢复工作区域大小
- 需配合"避免全屏助手"功能使用
- 用户可独立控制白板模式的全屏行为

Ink Canvas/MainWindow_cs/MW_Settings.cs

@@ -2182,6 +2182,7 @@ namespace Ink_Canvas
             Settings.Advanced.EdgeGestureUtilOnlyAffectBlackboardMode = false;
             Settings.Advanced.IsEnableFullScreenHelper = false;
             Settings.Advanced.IsEnableAvoidFullScreenHelper = false;
+            Settings.Advanced.IsEnableAvoidFullScreenHelperForWhiteboard = false;
             Settings.Advanced.IsEnableForceFullScreen = false;
             Settings.Advanced.IsEnableDPIChangeDetection = false;
             Settings.Advanced.IsEnableResolutionChangeDetection = false;
@@ -2442,6 +2443,13 @@ namespace Ink_Canvas
             }
         }
 
+        private void ToggleSwitchIsEnableAvoidFullScreenHelperForWhiteboard_OnToggled(object sender, RoutedEventArgs e)
+        {
+            if (!isLoaded) return;
+            Settings.Advanced.IsEnableAvoidFullScreenHelperForWhiteboard = ToggleSwitchIsEnableAvoidFullScreenHelperForWhiteboard.IsOn;
+            SaveSettingsToFile();
+        }
+
         private void ToggleSwitchIsEnableEdgeGestureUtil_Toggled(object sender, RoutedEventArgs e)
         {
             if (!isLoaded) return;