Function PickerSelectionFooter 

pub(crate) fn PickerSelectionFooter(
    props: PickerSelectionFooterProps,
) -> impl IntoView

多选模式底栏：已选计数、清空与确认插入。

Required Props

• selected: [RwSignal<Vec<AssetSelection>>]
• on_pick: impl Into<Callback<Vec<AssetSelection>>>