Error handling

Don't erase everything after the error is placed, rather display it after 2-3 seconds. so error only when = pressed

Look at the Kivy UI code that handles the '=' button press and error display. The error message should persist for 2-3 seconds before clearing, instead of being erased immediately. Find where the error is shown and add a timer or schedule a function to clear it after a delay. Test by triggering an error and verifying the message disappears automatically.

索引モデルが issue の本文から書いたものです。