refactor(主题): 将主题相关逻辑提取到ThemeHelper类中

重构主题相关代码，将重复的IsSystemThemeLight方法和主题应用逻辑提取到新的ThemeHelper工具类中
简化多个窗口的主题处理代码，统一使用ThemeHelper进行主题管理

Ink Canvas/Windows/RandWindow.xaml.cs

@@ -79,60 +79,16 @@ namespace Ink_Canvas
 
         private void ApplyTheme(Settings settings)
         {
-            try
+            ThemeHelper.ApplyTheme(this, settings, theme =>
             {
-                if (settings.Appearance.Theme == 0) // 浅色主题
-                {
-                    iNKORE.UI.WPF.Modern.ThemeManager.SetRequestedTheme(this, iNKORE.UI.WPF.Modern.ElementTheme.Light);
-                }
-                else if (settings.Appearance.Theme == 1) // 深色主题
-                {
-                    iNKORE.UI.WPF.Modern.ThemeManager.SetRequestedTheme(this, iNKORE.UI.WPF.Modern.ElementTheme.Dark);
-                }
-                else // 跟随系统主题
-                {
-                    bool isSystemLight = IsSystemThemeLight();
-                    if (isSystemLight)
-                    {
-                        iNKORE.UI.WPF.Modern.ThemeManager.SetRequestedTheme(this, iNKORE.UI.WPF.Modern.ElementTheme.Light);
-                    }
-                    else
-                    {
-                        iNKORE.UI.WPF.Modern.ThemeManager.SetRequestedTheme(this, iNKORE.UI.WPF.Modern.ElementTheme.Dark);
-                    }
-                }
-
-                // 根据主题设置窗口背景
                 if (settings.RandSettings.SelectedBackgroundIndex <= 0)
                 {
-                    // 没有自定义背景时，使用主题背景色
                     if (Application.Current.FindResource("RandWindowBackground") is SolidColorBrush backgroundBrush)
                     {
                         MainBorder.Background = backgroundBrush;
                     }
                 }
-            }
-            catch (Exception ex)
-            {
-                LogHelper.WriteLogToFile($"应用点名窗口主题出错: {ex.Message}", LogHelper.LogType.Error);
-            }
-        }
-
-        private bool IsSystemThemeLight()
-        {
-            var light = false;
-            try
-            {
-                var registryKey = Microsoft.Win32.Registry.CurrentUser;
-                var themeKey =
-                    registryKey.OpenSubKey("software\\Microsoft\\Windows\\CurrentVersion\\Themes\\Personalize");
-                var keyValue = 0;
-                if (themeKey != null) keyValue = (int)themeKey.GetValue("SystemUsesLightTheme");
-                if (keyValue == 1) light = true;
-            }
-            catch (Exception ex) { System.Diagnostics.Debug.WriteLine(ex); }
-
-            return light;
+            });
         }
 
         public RandWindow(Settings settings, bool IsAutoClose)