Faint text was painted as its ink at 66% alpha over the cell. On a light
background that fixed fade collapses the WCAG ratio: Catppuccin Latte's
foreground fell from 7.06:1 to 3.18:1, Rose Pine Dawn's to 3.08:1, and
every bright-black the palette rescue had lifted to 4.5:1 fell back to
~2.5:1 on all four light builtins (#858).
On a light cell the fade is now walked back toward the ink until it clears
the 4.5:1 text floor, capped at the ink's own ratio. Dark cells, and the
legible-palette switch turned off, keep the plain fade byte-for-byte.
Fixes#858
Claude-Session: https://claude.ai/code/session_01JRqYZ9E153WpSHGS2AW3BM