The YAML frontmatter was scaffolding for the impeccable design skill,
which was removed in 3d16c75f. Nothing read it since, and it had already
drifted from lib/const/settings.dart (tokens that don't exist in code,
missing ones that do). Drop it and point at settings.dart as the only
source of truth. Keep the named rules and the ShadDialog gotcha, fold the
type roles and spacing steps into prose, add defender blue to the
tactical semantics, and name the canvas gradients that are intentional so
nobody strips them as violations.

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