Fix UnboundLocalError: remove redundant os import in exception handler

src/context_manager.py

@@ -67,7 +67,7 @@ class EfficientContextManager:
                 db_path = settings.db_path
             except (ImportError, AttributeError):
                 # Fallback: check environment variable or use /tmp
-                import os
+                # os is already imported at top of file
                 db_path = os.getenv("DB_PATH", "/tmp/sessions.db")
         self.db_path = db_path
         # Ensure directory exists