chore(deps): update pyjwt requirement in /backend

Updates the requirements on [pyjwt](https://github.com/jpadilla/pyjwt) to permit the latest version.
- [Release notes](https://github.com/jpadilla/pyjwt/releases)
- [Changelog](https://github.com/jpadilla/pyjwt/blob/master/CHANGELOG.rst)
- [Commits](jpadilla/pyjwt@2.8.0...2.12.1)

---
updated-dependencies:
- dependency-name: pyjwt
  dependency-version: 2.12.1
  dependency-type: direct:production
...

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

Author: dependabot[bot]

backend/requirements.txt

@@ -31,7 +31,7 @@ aiofiles>=24.0.0
 
 # Supabase (postgrest-py handled as dependency)
 supabase>=2.0.0
-pyjwt>=2.8.0  # JWT token verification for Supabase Auth
+pyjwt>=2.12.1  # JWT token verification for Supabase Auth
 
 # Testing
 pytest>=8.0.0