refactor: 优化后端认证和路由功能

- 优化auth.py认证路由
- 优化books.py书籍路由
- 优化sms_service.py短信服务

api/routers/books.py

@@ -21,7 +21,7 @@ async def get_current_book(
     db: AsyncSession = Depends(get_async_db)
 ):
     """获取当前回忆录（需要认证）"""
-    stmt = select(BookModel).where(BookModel.user_id == current_user.id).order_by(BookModel.updated_at.desc())
+    stmt = select(BookModel).where(BookModel.user_id == current_user.id).order_by(BookModel.updated_at.desc()).limit(1)
     result = await db.execute(stmt)
     book = result.scalar_one_or_none()
     
@@ -45,7 +45,7 @@ async def clear_book_update(
     db: AsyncSession = Depends(get_async_db),
 ):
     """清除回忆录更新标记"""
-    stmt = select(BookModel).where(BookModel.user_id == current_user.id).order_by(BookModel.updated_at.desc())
+    stmt = select(BookModel).where(BookModel.user_id == current_user.id).order_by(BookModel.updated_at.desc()).limit(1)
     result = await db.execute(stmt)
     book = result.scalar_one_or_none()
     if not book: