fix: rename stale OpenaiConfig references to APIServerConfig

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.

atroposlib/tests/test_env_imports.py

@@ -0,0 +1,22 @@
+"""Regression tests for environment module imports.
+
+Ensures every environment module can be imported without errors
+(e.g. no stale references to renamed symbols like OpenaiConfig).
+"""
+
+import importlib
+
+import pytest
+
+
+@pytest.mark.parametrize(
+    "module_path",
+    [
+        "environments.sft_loader_server",
+        "environments.community.ufc_prediction_env.ufc_server",
+        "environments.community.ufc_prediction_env.ufc_image_env",
+    ],
+)
+def test_environment_module_imports(module_path):
+    """Each environment module should import without ImportError."""
+    importlib.import_module(module_path)