fix: 增加分页参数page_size上限到500

任务中心需要加载全部用户列表，将限制从100提升到500

backend/app/schemas/base.py

@@ -42,7 +42,7 @@ class PaginationParams(BaseModel):
     """分页参数"""
 
     page: int = Field(default=1, ge=1, description="页码")
-    page_size: int = Field(default=20, ge=1, le=100, description="每页数量")
+    page_size: int = Field(default=20, ge=1, le=500, description="每页数量")
 
     @property
     def offset(self) -> int: