Bump mongoose from 8.16.1 to 9.6.2 in /backend

Bumps [mongoose](https://github.com/Automattic/mongoose) from 8.16.1 to 9.6.2.
- [Release notes](https://github.com/Automattic/mongoose/releases)
- [Changelog](https://github.com/Automattic/mongoose/blob/master/CHANGELOG.md)
- [Commits](Automattic/mongoose@8.16.1...9.6.2)

---
updated-dependencies:
- dependency-name: mongoose
  dependency-version: 9.6.2
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

backend/package-lock.json

@@ -27,7 +27,7 @@
     "form-data": "^4.0.4",
     "formdata-node": "^6.0.3",
     "groq-sdk": "^0.3.0",
-    "mongoose": "^8.0.1",
+    "mongoose": "^9.6.2",
     "morgan": "^1.10.1",
     "multer": "^2.0.2",
     "openai": "^4.20.1",