Fix: Corrected type hint in schemas.py for Python 3.9 (Optional[str]) and confirmed typing import

app/schemas.py

@@ -9,7 +9,7 @@ class GenerateRequest(BaseModel): # <--- 'GenerateRequest' 정의되어 있음
 class GenerateResponse(BaseModel): # <--- 'GenerateResponse' 정의되어 있음
     generated_prompt: str
     processing_time_seconds: float
-    error_message: str | None = None
+    error_message: Optional[str] = None # <--- 이렇게 변경되었는지 확인!
 
 class ResetMemoryResponse(BaseModel): # <--- 'ResetMemoryResponse' 정의되어 있음
     message: str