Fix Fyne threading error by using async Do() instead of DoAndWait()

The setContent function was calling fyne.DoAndWait() from the main goroutine,
which created a deadlock. Changed to use fyne.Do() (asynchronous) to properly
marshal UI updates without blocking.

This resolves the error:
  'fyne.Do[AndWait] called from main goroutine'

The async approach is correct here since we don't need to wait for the
content update to complete before continuing.

main.go

@@ -346,8 +346,8 @@ func (s *appState) setContent(body fyne.CanvasObject) {
 		s.window.SetContent(container.NewMax(bg, body))
 	}
 
-	// Always marshal content changes onto the Fyne UI thread
-	fyne.DoAndWait(update)
+	// Use async Do() instead of DoAndWait() to avoid deadlock when called from main goroutine
+	fyne.Do(update)
 }
 
 // showErrorWithCopy displays an error dialog with a "Copy Error" button