fix: add @objectstack/spec as a devDependency in package.json and pnpm-lock.yaml

Author: hotlong

apps/docs/package.json

@@ -25,6 +25,7 @@
     "tailwind-merge": "^3.4.0"
   },
   "devDependencies": {
+    "@objectstack/spec": "workspace:*",
     "@tailwindcss/postcss": "^4.1.18",
     "@tailwindcss/typography": "^0.5.19",
     "@types/mdx": "^2.0.13",