chore(deps): bump bcrypt from 4.3.0 to 5.0.0 in /backend

Bumps [bcrypt](https://github.com/pyca/bcrypt) from 4.3.0 to 5.0.0.
- [Changelog](https://github.com/pyca/bcrypt/blob/main/CHANGELOG.rst)
- [Commits](https://github.com/pyca/bcrypt/compare/4.3.0...5.0.0)

---
updated-dependencies:
- dependency-name: bcrypt
  dependency-version: 5.0.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

backend/requirements.txt

@@ -13,7 +13,7 @@ asyncpg==0.31.0
 # Authentication
 
 python-jose[cryptography]==3.5.0  # Updated: Fixed algorithm confusion with OpenSSH ECDSA keys (was 3.3.0)
-bcrypt==4.3.0
+bcrypt==5.0.0
 python-multipart==0.0.22  # Updated: Fixed multiple vulnerabilities (was 0.0.6)
 authlib==1.6.9  # Updated: Fixed OIDC hash binding, JWE RSA1_5 padding oracle, alg:none bypass, JWK header injection (was 1.6.6)
 httpx==0.26.0