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/MainWindow_cs/MW_AutoTheme.cs

@@ -1,4 +1,5 @@
 using iNKORE.UI.WPF.Modern;
+using Ink_Canvas.Helpers;
 using Microsoft.Win32;
 using System;
 using System.Collections.Generic;
@@ -246,27 +247,11 @@ namespace Ink_Canvas
                     SetTheme(ThemeDark);
                     break;
                 case 2:
-                    SetTheme(IsSystemThemeLight() ? ThemeLight : ThemeDark);
+                    SetTheme(ThemeHelper.IsSystemThemeLightLegacy() ? ThemeLight : ThemeDark);
                     break;
             }
         }
 
-        private bool IsSystemThemeLight()
-        {
-            try
-            {
-                var registryKey = Registry.CurrentUser;
-                var themeKey = registryKey.OpenSubKey("software\\Microsoft\\Windows\\CurrentVersion\\Themes\\Personalize");
-                if (themeKey != null)
-                {
-                    int keyValue = (int)themeKey.GetValue("SystemUsesLightTheme");
-                    return keyValue == 1;
-                }
-            }
-            catch (Exception ex) { System.Diagnostics.Debug.WriteLine(ex); }
-            return false;
-        }
-
         private void AutoSwitchFloatingBarIconForTheme(string theme)
         {
             try