The canonical colors.toml keys are now background/foreground, including
all permutations (dark_background, darker_background, lighter_background,
dark_foreground, light_foreground, bright_foreground). The old short
names are gone entirely, not kept as aliases; legacy alacritty-generated
themes still resolve through the ANSI color0/color7 fallback.
Theme files are also regrouped: accent/selection/muted first, then the
backgrounds, then the foregrounds, then the named colors.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Based entirely on the work of @robzolkos in #5711. That attempt was
adapted to better fit the standard templating system while also adding
color mixing for use in other themes.
