chore(deps): bump cffi from 2.1.0 to 2.1.1 in /backend

Bumps [cffi](https://github.com/python-cffi/cffi) from 2.1.0 to 2.1.1.
- [Release notes](https://github.com/python-cffi/cffi/releases)
- [Commits](python-cffi/cffi@v2.1.0...v2.1.1)

---
updated-dependencies:
- dependency-name: cffi
  dependency-version: 2.1.1
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

backend/requirements.txt

@@ -57,7 +57,7 @@ certifi==2026.7.22
     #   httpcore
     #   httpx
     #   requests
-cffi==2.1.0
+cffi==2.1.1
     # via cryptography
 charset-normalizer==3.4.9
     # via requests