Function render_to_buffer 

pub fn render_to_buffer(entries: &[FileTreeEntry], _nerd_fonts: bool) -> Buffer

Serialise the entry list to a Buffer. Each row is <indent><marker><icon><name> where <marker> is ▾ for an expanded dir, ▸ for a collapsed dir, and for a file. Indent is two spaces per depth. The <icon> glyph comes from lattice_core::ui::icons::glyph_for_entry – nerd-fonts when nerd_fonts is true, the BMP-block fallback palette otherwise. Both palettes occupy two cells, so column geometry is the same either way.