Fix CBT history react-markdown crash, fix test deletion cascade, fix cbt theme, add 180 NEET questions

package.json

@@ -18,6 +18,7 @@
     "katex": "^0.17.0",
     "lucide-react": "^1.21.0",
     "next": "16.2.9",
+    "next-themes": "^0.4.6",
     "react": "19.2.4",
     "react-datepicker": "^9.1.0",
     "react-dom": "19.2.4",
@@ -28,6 +29,7 @@
     "rehype-raw": "^7.0.0",
     "remark-math": "^6.0.0",
     "tailwind-merge": "^3.6.0",
+    "zod": "^4.4.3",
     "zustand": "^5.0.14"
   },
   "devDependencies": {