Download libnccl2 .deb from NVIDIA's CUDA apt repo (Debian 12) during ISO
build, extract libnccl.so.* into the overlay at /usr/lib/ alongside
libnvidia-ml and libcuda. Version pinned in VERSIONS, reflected in
/etc/bee-release.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>