添加单实例限制、应用图标、移除托盘设置菜单、快捷键暂停/恢复功能

单实例限制：通过命名Mutex和窗口消息广播确保只能运行一个实例，再次启动时唤起已有窗口

应用图标：exe文件嵌入app.ico，托盘和窗口图标统一使用该图标文件

移除托盘右键菜单中与显示主界面重复的设置选项

快捷键暂停/恢复：托盘菜单和主界面侧边栏均添加切换按钮，通过MainViewModel.IsHotKeyEnabled双向同步

PersonalToolBox/App.xaml.cs

@@ -1,4 +1,6 @@
 using System.IO;
+using System.Runtime.InteropServices;
+using System.Threading;
 using System.Windows;
 using Microsoft.Extensions.DependencyInjection;
 using PersonalToolBox.Services;
@@ -17,6 +19,17 @@ public partial class App : System.Windows.Application
         Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
         "PersonalToolBox", "crash.log");
 
+    private const string AppMutexName = "PersonalToolBox_SingleInstance_8E2F4A1C";
+    private static Mutex? _mutex;
+
+    [DllImport("user32.dll")]
+    private static extern uint RegisterWindowMessage(string lpString);
+
+    [DllImport("user32.dll")]
+    private static extern bool PostMessage(IntPtr hWnd, uint Msg, IntPtr wParam, IntPtr lParam);
+
+    private static readonly IntPtr HWND_BROADCAST = new IntPtr(0xFFFF);
+
     public App()
     {
         // 监听未处理的异常，写入文件日志
@@ -36,6 +49,15 @@ public partial class App : System.Windows.Application
 
     protected override async void OnStartup(StartupEventArgs e)
     {
+        _mutex = new Mutex(true, AppMutexName, out bool createdNew);
+        if (!createdNew)
+        {
+            uint msg = RegisterWindowMessage("PersonalToolBox_ShowMain");
+            PostMessage(HWND_BROADCAST, msg, IntPtr.Zero, IntPtr.Zero);
+            Shutdown();
+            return;
+        }
+
         try
         {
             base.OnStartup(e);