The blink-off clear erased the cursor cell's selection tint, custom
background, and underline decorations, and compressed double-width
glyphs into a single cell. Repaint the full layer stack in row-renderer
order across the wide-glyph extent, and strengthen the blink-off tests
to assert paint order, colors, and two-cell extents.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>