chore(deps): bump multer from 2.0.2 to 2.1.1 in /backend

Bumps [multer](https://github.com/expressjs/multer) from 2.0.2 to 2.1.1.
- [Release notes](https://github.com/expressjs/multer/releases)
- [Changelog](https://github.com/expressjs/multer/blob/main/CHANGELOG.md)
- [Commits](expressjs/multer@v2.0.2...v2.1.1)

---
updated-dependencies:
- dependency-name: multer
  dependency-version: 2.1.1
  dependency-type: direct:production
...

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

Author: dependabot[bot]

backend/package-lock.json

@@ -30,7 +30,7 @@
     "express-rate-limit": "^7.5.0",
     "express-validator": "^7.3.0",
     "jsonwebtoken": "^9.0.2",
-    "multer": "^2.0.2",
+    "multer": "^2.1.1",
     "obs-websocket-js": "^5.0.6",
     "socket.io": "^4.8.1",
     "uuid": "^11.1.0",