Function create_empty_workspace 

async fn create_empty_workspace(
    state: &AppState,
    name: &str,
) -> Result<String, String>

A workspace with no tabs yet, for “Open in a new window”: unlike CreateWindow’s fresh workspace it gets no default tab, so the new window shows only the layout. The caller opens the window onto it afterwards (the host’s open_new_window { workspace_id }, the tear-off attach path).