Render the keystroke badge and step caption as a solid yellow rectangle
with no border glyphs and a one-cell text margin, instead of a
rounded-border box — deliberately unlike the app's bordered panels so
the demo overlays read as a distinct, eye-catching callout. Shared
fill_overlay_rect helper (borderless Block fill + inset Paragraph).
Snapshots regenerated; ADR-0047 D4 wording updated.