Enhance chatbot conversation engine and add retrieval eval suite

package.json

@@ -10,7 +10,8 @@
     "build": "tsc -b && vite build",
     "start": "node --env-file=.env server.js",
     "lint": "eslint .",
-    "preview": "vite preview"
+    "preview": "vite preview",
+    "chatbot:eval": "node scripts/evaluate-chatbot.mjs"
   },
   "dependencies": {
     "express": "^5.2.1",