fix(roi):修复 working_hours 为空数组 [] 时被错误识别为 None 的问题，导致全天模式失效。

- 修改 `api/roi.py` 中的判断逻辑：使用 `is not None` 替代 truthy 检查，确保 `[]` 能正确序列化并存入数据库
- 更新 `config.yaml` 全局默认值为 `working_hours: []`，表示“全天开启”

api/roi.py

@@ -108,7 +108,7 @@ def add_roi(
 ):
     import json
 
-    working_hours_json = json.dumps(request.working_hours) if request.working_hours else None
+    working_hours_json = json.dumps(request.working_hours) if request.working_hours is not None else None
 
     roi = create_roi(
         db,
@@ -153,7 +153,7 @@ def modify_roi(
     db: Session = Depends(get_db),
 ):
     import json
-    working_hours_json = json.dumps(request.working_hours) if request.working_hours else None
+    working_hours_json = json.dumps(request.working_hours) if request.working_hours is not None else None
 
     roi = update_roi(
         db,