Adds the Mappe design handoff as in-repo ground truth and closes out the design-token foundation: --radius-sm/md/full + --shadow-sm/md tokens (distinct dark values in both dark blocks) and the canonical 10-color $lib/shared/avatarPalette.ts (AA-darkened sage/amber/sand swatches), guarded by avatarPalette.spec.ts. Closes#854.
