chore(design-system): add extraction artifact and token drift gate

Record the design decisions actually in use and add a static gate that blocks new bare colors, bare sizes, important overrides, and wb token definitions outside token sources.

package.json

@@ -31,6 +31,7 @@
     "sandbox:maintain": "node scripts/sandbox-maintain.mjs",
     "start": "electron-vite preview",
     "typecheck": "tsc --noEmit -p tsconfig.node.json && tsc --noEmit -p tsconfig.web.json",
+    "check:tokens": "node scripts/check-design-tokens.mjs",
     "test:settings-performance": "node scripts/verify-settings-performance.cjs",
     "models:sync-metadata": "node scripts/sync-model-metadata.mjs",
     "test:custom-models": "esbuild scripts/custom-model-regression.ts --bundle --platform=node --format=esm --outfile=.tmp/custom-model-regression.mjs --log-level=warning && node .tmp/custom-model-regression.mjs",