Make personal configs optional in SGLang's official docker image. (#16365)

docker/Dockerfile

@@ -411,11 +411,12 @@ RUN sh -c "$(curl --retry 3 --retry-delay 2 -fsSL https://raw.githubusercontent.
     && git clone --depth 1 https://github.com/zsh-users/zsh-autosuggestions ${ZSH_CUSTOM:-~/.oh-my-zsh/custom}/plugins/zsh-autosuggestions \
     && git clone --depth 1 https://github.com/zsh-users/zsh-syntax-highlighting.git ${ZSH_CUSTOM:-~/.oh-my-zsh/custom}/plugins/zsh-syntax-highlighting
 
+# These configs are optional; users can override them by mounting their own files
+COPY docker/configs/opt/.vimrc /opt/sglang/.vimrc
+COPY docker/configs/opt/.tmux.conf /opt/sglang/.tmux.conf
+COPY docker/configs/opt/.gitconfig /opt/sglang/.gitconfig
+
 # Configure development environment
-COPY docker/configs/.vimrc /root/.vimrc
-COPY docker/configs/.tmux.conf /root/.tmux.conf
-COPY docker/configs/.gitconfig /tmp/.gitconfig
-RUN cat /tmp/.gitconfig >> /root/.gitconfig && rm /tmp/.gitconfig
 COPY docker/configs/.zshrc /root/.zshrc
 
 # Fix Triton to use system ptxas for Blackwell (sm_103a) support (CUDA 13+ only)