Function render_sidebar_rows 

pub fn render_sidebar_rows(
    entries: &[StatusEntry],
    staged: &HashSet<String>,
    selected: usize,
) -> Vec<SidebarRow>

Build the sidebar rows. staged marks paths with [S] (whatever the user has staged via toggle_stage); unmerged entries always get [U]. Order follows the input entries (which is git status porcelain order).