chore(deps): bump cryptography from 46.0.7 to 48.0.0 in /backend (#245)

Bumps [cryptography](https://github.com/pyca/cryptography) from 46.0.7 to 48.0.0.
- [Changelog](https://github.com/pyca/cryptography/blob/main/CHANGELOG.rst)
- [Commits](https://github.com/pyca/cryptography/compare/46.0.7...48.0.0)

---
updated-dependencies:
- dependency-name: cryptography
  dependency-version: 48.0.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

backend/requirements.txt

@@ -38,7 +38,7 @@ celery==5.6.3
 redis==7.4.0
 
 # Security & Encryption
-cryptography==46.0.7  # Updated: Fixed NULL pointer dereference (was 42.0.0)
+cryptography==48.0.0  # Updated: Fixed NULL pointer dereference (was 42.0.0)
 
 # Notifications
 apprise==1.9.9