fix(release): 支持单文件发布产物

改为从应用程序自身提取托盘图标，移除发布目录中的外部 app.ico 依赖。
确保 v0.1.0 发布目录只包含 OmniNotify.exe，便于手动上传到 Gitea Release。

App.xaml.cs

@@ -86,10 +86,9 @@ public partial class App : System.Windows.Application
 
     private void CreateTrayIcon()
     {
-        var iconPath = Path.Combine(AppContext.BaseDirectory, "app.ico");
         _notifyIcon = new Forms.NotifyIcon
         {
-            Icon = new System.Drawing.Icon(iconPath),
+            Icon = System.Drawing.Icon.ExtractAssociatedIcon(Environment.ProcessPath ?? "") ?? System.Drawing.SystemIcons.Application,
             Text = "Omni-Notify",
             Visible = true
         };

OmniNotify.csproj

@@ -10,8 +10,4 @@
     <ApplicationIcon>app.ico</ApplicationIcon>
   </PropertyGroup>
 
-  <ItemGroup>
-    <Content Include="app.ico" CopyToOutputDirectory="PreserveNewest" />
-  </ItemGroup>
-
 </Project>