Three environment files still imported the old `OpenaiConfig` name,
which was renamed to `APIServerConfig`. This causes an ImportError
at module load time, making these environments unusable:
- environments/sft_loader_server.py
- environments/community/ufc_prediction_env/ufc_server.py
- environments/community/ufc_prediction_env/ufc_image_env.py
Also adds a lightweight import regression test.
