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/services/sms_service.py

@@ -166,7 +166,7 @@ async def check_rate_limit(db: AsyncSession, phone: str) -> Tuple[bool, int]:
         SmsVerificationCode.phone == phone
     ).order_by(
         SmsVerificationCode.created_at.desc()
-    )
+    ).limit(1)
     result = await db.execute(stmt)
     recent_code = result.scalar_one_or_none()
     
@@ -262,7 +262,7 @@ async def verify_code(
         SmsVerificationCode.is_expired == False
     ).order_by(
         SmsVerificationCode.created_at.desc()
-    )
+    ).limit(1)
     result = await db.execute(stmt)
     verification = result.scalar_one_or_none()