FfmpegProgress::Ansi

ASCII fallback for terminals whose locale isn't UTF-8 — the empty/full cells are still distinguishable without any non-ASCII bytes.

Foreground green + background gray (bright black). The gray background is critical: partial Unicode blocks are left-aligned glyphs, so the right portion of a partial cell shows the background — making it gray so the bar has no gap between the filled and unfilled portions.

Best-effort detection of whether the controlling locale will render Unicode block characters. Returns true if LC_ALL / LC_CTYPE / LANG advertises UTF-8 (case-insensitive). A wholly unset locale defaults to true since modern interactive terminals are UTF-8.