Design system: document the world; tabular numerals on measured values

- Add the documented design system (DESIGN.md + .impeccable/design.json):
  35 tokens, the seven named rules, and the motion and elevation values.
- Fix a real craft-floor miss the documentation surfaced: measured values and
  prices now carry font-variant-numeric: tabular-nums, so columns of digits
  line up instead of shipping browser defaults.
- Two bespoke fluid font sizes moved onto the documented ramp, and a dead
  token removed. The detector is clean.

Author: RelayStack

.gitignore

@@ -12,5 +12,8 @@ dist/
 .impeccable/build/
 
 # Development-only: Impeccable artifacts and the local screenshot helper
-.impeccable/
+# Development-only Impeccable artifacts. The documented design system ships;
+# mocks, review captures, build state and the direction contract do not.
+.impeccable/*
+!.impeccable/design.json
 scripts/shoot.mjs