chore(deps): bump python-multipart from 0.0.17 to 0.0.18 in /backend

Bumps [python-multipart](https://github.com/Kludex/python-multipart) from 0.0.17 to 0.0.18.
- [Release notes](https://github.com/Kludex/python-multipart/releases)
- [Changelog](https://github.com/Kludex/python-multipart/blob/master/CHANGELOG.md)
- [Commits](https://github.com/Kludex/python-multipart/compare/0.0.17...0.0.18)

---
updated-dependencies:
- dependency-name: python-multipart
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

backend/requirements.txt

@@ -1,7 +1,7 @@
 fastapi==0.111.0
 uvicorn[standard]==0.30.6
 pydantic==2.9.2
-python-multipart==0.0.17
+python-multipart==0.0.18
 
 Flask==3.0.3
 Flask-Cors==5.0.0