docs(engineering): add project audit report and improvement plan

This commit introduces a comprehensive engineering audit report for the Tootaio Studio project. The report is structured into documents covering architecture, code quality, performance, security, CI/CD, and
observability. It also includes a phased improvement roadmap and a set of `.patch` files to apply immediate fixes for content schemas, package scripts, and CI configuration.

docs/20251106/patches/0002-package-scripts.patch

@@ -0,0 +1,39 @@
+diff --git a/package.json b/package.json
+--- a/package.json
++++ b/package.json
+@@
+   "scripts": {
+-    "build": "nuxt build",
+-    "dev": "nuxt dev",
+-    "generate": "nuxt generate",
+-    "preview": "nuxt preview",
+-    "postinstall": "nuxt prepare"
++    "build": "nuxt build",
++    "dev": "nuxt dev",
++    "generate": "nuxt generate",
++    "preview": "nuxt preview",
++    "postinstall": "nuxt prepare",
++    "typecheck": "nuxt typecheck",
++    "lint": "eslint --ext .ts,.js,.mjs,.vue --ignore-path .gitignore .",
++    "lint:fix": "pnpm lint -- --fix",
++    "check": "pnpm lint && pnpm typecheck && pnpm build"
+   },
+@@
+   "dependencies": {
+     "@iconify-json/mdi": "^1.2.3",
+     "@nuxt/content": "3.8.0",
+     "@nuxt/eslint": "1.10.0",
+     "@nuxt/ui": "4.1.0",
+     "@nuxtjs/i18n": "10.2.0",
+     "@nuxtjs/seo": "3.2.2",
+     "better-sqlite3": "^12.4.1",
+     "eslint": "^9.39.0",
+     "nuxt": "^4.2.0",
+     "typescript": "^5.9.3",
+     "vue": "^3.5.22",
+     "vue-router": "^4.6.3"
+-  }
++  },
++  "engines": {
++    "node": ">=18.20.0"
++  }