Refactor code structure for improved readability and maintainability

backend/app/api/models/document.py

@@ -1,4 +1,3 @@
-# src/api/models/document.py
 """文档相关Pydantic数据模型"""
 
 from pydantic import BaseModel, Field
@@ -60,4 +59,4 @@ class ErrorResponse(BaseModel):
     """错误响应"""
     error: str = Field(..., description="错误类型")
     message: str = Field(..., description="错误消息")
-    timestamp: datetime = Field(default_factory=datetime.now, description="时间戳")
+    timestamp: datetime = Field(default_factory=datetime.now, description="时间戳")