657aad6cf0
Replace --bui-surface-1..5 with --bui-bg-neutral-1..5 for both light and dark themes. --bui-bg-neutral-1 replaces the deprecated --bui-bg-app, and --bui-bg-neutral-2..5 extend the scale. The old bare --bui-bg-neutral-1..4 entries are removed from the deprecated section since their names are now reused; the hover/pressed/disabled variants remain deprecated. Updates colors.stories.tsx, the ESLint rule and tests, and all migration documentation and the PR description accordingly. Signed-off-by: Charles de Dreuille <charles.dedreuille@gmail.com>