修复错题一直显示处理中：超时、自动刷新与状态更新。

backend/app/core/config.py

@@ -19,6 +19,9 @@ class Settings(BaseSettings):
     FRONTEND_DIST: str = "../frontend/dist"
     ADMIN_DEFAULT_USERNAME: str = "admin"
     ADMIN_DEFAULT_PASSWORD: str = "admin123"
+    OCR_TIMEOUT_SECONDS: int = 300
+    AI_TIMEOUT_SECONDS: int = 600
+    PROCESS_STALE_MINUTES: int = 20
 
     class Config:
         env_file = ".env"