Function mode_buttons 

fn mode_buttons<M>(
    mode: RwSignal<M>,
    items: Vec<(M, &'static str)>,
    on_pick: Callback<M>,
) -> impl IntoView
where
    M: Copy + PartialEq + Send + Sync + 'static,

形态切换按钮组；点击先写入 mode，再回调 on_pick 处理附带状态。