Function on_carriage_press_window 

pub fn on_carriage_press_window(
    e: On<'_, '_, PointerPress>,
    q_carriages: Query<'_, '_, &TrainMember, With<Carriage>>,
    next_state: ResMut<'_, NextState<UiState>>,
)

Observer that runs on left click on carriages and opens the train window