Function render_overview 

pub fn render_overview(
    disks: &[PhysicalDisk],
    width: usize,
    color: bool,
) -> String

Render an at-a-glance overview comparing the physical disks’ capacities — a horizontal bar chart, one disk per line, each bar’s length proportional to that disk’s size relative to the largest, so the biggest disk fills the row and the rest read as fractions of it. Each line also shows the absolute size and the disk’s share of total storage. Synthesized disks (APFS containers, device-mapper) are excluded because they overlay physical space rather than add to it. Returns empty when fewer than two physical disks exist.