Function repository_get_downloaded_items 

pub async fn repository_get_downloaded_items(
    manager: State<'_, RepositoryManagerWrapper>,
    handle: String,
    parent_id: String,
    options: Option<GetItemsOptions>,
) -> Result<SearchResult, String>

Downloaded-only browse: items under a container that are on the device.

TRACES: UR-055 | DR-082, DR-083