Function run_picker 

pub fn run_picker<T: PickerItem>(
    items: Vec<T>,
    config: PickerConfig<'_>,
) -> Result<Option<T>>

Run the picker with stderr as the TUI backend. Stdout stays untouched so callers like tmx worktree list can print the selection on stdout for $(...) capture. Also avoids a macOS-specific freeze observed when rendering to stdout inside a tmux popup.