build: 更新Dockerfile中的阿里云镜像源配置

将sed替换方式改为直接写入完整的sources.list内容，确保使用阿里云镜像源

Dockerfile.backend

@@ -10,8 +10,9 @@ ENV DEBIAN_FRONTEND=noninteractive \
     PIP_INDEX_URL=https://pypi.tuna.tsinghua.edu.cn/simple \
     PIP_TRUSTED_HOST=pypi.tuna.tsinghua.edu.cn
 
-RUN sed -i 's/deb.debian.org/mirrors.aliyun.com/g' /etc/apt/sources.list \
-    && sed -i 's/security.debian.org/mirrors.aliyun.com/g' /etc/apt/sources.list \
+RUN echo 'deb http://mirrors.aliyun.com/debian/ bookworm main non-free contrib' > /etc/apt/sources.list \
+    && echo 'deb http://mirrors.aliyun.com/debian/ bookworm-updates main non-free contrib' >> /etc/apt/sources.list \
+    && echo 'deb http://mirrors.aliyun.com/debian-security/ bookworm-security main non-free contrib' >> /etc/apt/sources.list \
     && apt-get update && apt-get install -y --no-install-recommends \
     build-essential \
     gcc \