fix(docker): make ubuntu apt mirror optional

Dockerfile

@@ -1,6 +1,6 @@
 FROM smanx/opencode:latest AS base
 USER root
-ARG UBUNTU_APT_MIRROR=mirrors.aliyun.com
+ARG UBUNTU_APT_MIRROR=
 ARG PYPI_INDEX_URL=https://pypi.tuna.tsinghua.edu.cn/simple
 ARG PYPI_TRUSTED_HOST=pypi.tuna.tsinghua.edu.cn
 ENV VIRTUAL_ENV=/opt/venv
@@ -11,8 +11,10 @@ ENV UV_INDEX_URL=${PYPI_INDEX_URL}
 
 COPY vendor/bun-linux-x64.zip /tmp/bun.zip
 
-RUN sed -i "s|http://archive.ubuntu.com|https://${UBUNTU_APT_MIRROR}|g; s|http://security.ubuntu.com|https://${UBUNTU_APT_MIRROR}|g" /etc/apt/sources.list 2>/dev/null || true && \
+RUN if [ -n "${UBUNTU_APT_MIRROR}" ]; then \
-    sed -i "s|http://archive.ubuntu.com|https://${UBUNTU_APT_MIRROR}|g; s|http://security.ubuntu.com|https://${UBUNTU_APT_MIRROR}|g" /etc/apt/sources.list.d/*.sources 2>/dev/null || true && \
+      sed -i "s|http://archive.ubuntu.com|https://${UBUNTU_APT_MIRROR}|g; s|http://security.ubuntu.com|https://${UBUNTU_APT_MIRROR}|g" /etc/apt/sources.list 2>/dev/null || true; \
+      sed -i "s|http://archive.ubuntu.com|https://${UBUNTU_APT_MIRROR}|g; s|http://security.ubuntu.com|https://${UBUNTU_APT_MIRROR}|g" /etc/apt/sources.list.d/*.sources 2>/dev/null || true; \
+    fi && \
     apt-get update && apt-get install -y --no-install-recommends \
     curl \
     jq \