added sending closing event message to settings windows (#7)

Reviewed-on: #7
Co-authored-by: Aleksandr Neychev <alexnejchev73@gmail.com>

CursorLang.Agent/Agent.cs

@@ -125,5 +125,12 @@ internal sealed class Agent : IDisposable
 
     private void OnOpenRequested(object? sender, EventArgs e) => SettingsLauncher.Open();
 
-    private void OnExitRequested(object? sender, EventArgs e) => _window.Quit();
+    // "Exit" means the application, not just the background half of it. A settings
+    // window left open would outlive the tray icon it was opened from, so it is asked
+    // to close first — it may be the very window the user is looking at
+    private void OnExitRequested(object? sender, EventArgs e)
+    {
+        SettingsCloseSignal.RequestClose();
+        _window.Quit();
+    }
 }