Step 12：后端轻量优化（API 稳定性 & 前端友好）

backend/app/schemas/common.py

@@ -0,0 +1,16 @@
+from typing import Generic, TypeVar
+
+from pydantic import BaseModel
+from pydantic.generics import GenericModel
+
+T = TypeVar("T")
+
+
+class PaginatedResponse(GenericModel, Generic[T]):
+    items: list[T]
+    total: int
+
+
+class MessageResponse(BaseModel):
+    code: str
+    message: str