feat(iso): split into nvidia and amd variants, fix KVM graphics and PATH

- build.sh: add --variant nvidia|amd; separate work dirs per variant
  (live-build-work-nvidia / live-build-work-amd); GPU-specific steps
  (modules, NCCL, cuBLAS, nccl-tests) run only for nvidia; deb package
  cache synced back to shared location after each lb build so second
  variant reuses downloaded packages; ISO output named
  easy-bee-{variant}-v{ver}-amd64.iso
- build-in-container.sh: add --variant nvidia|amd|all (default: all);
  runs build.sh twice in one container for 'all'; --clean-build wipes
  both variant work dirs
- package-lists: remove GPU packages from bee.list.chroot; add
  bee-nvidia.list.chroot (DCGM) and bee-amd.list.chroot (ROCm)
- 9000-bee-setup hook: read /etc/bee-gpu-vendor; enable bee-nvidia.service
  and DCGM only for nvidia; set up ROCm symlinks only for amd
- auto/config: --iso-volume uses BEE_GPU_VENDOR_UPPER env var
- grub.cfg: add nomodeset to EASY-BEE and EASY-BEE (load to RAM) entries
  — fixes X/lightdm on BMC KVM (ASPEED AST chip requires nomodeset for
  fbdev to work; NVIDIA H100 compute does not need KMS)
- bee.sh / smoketest.sh: add /usr/sbin to PATH so dmidecode, smartctl,
  nvme are found
- 9100-memtest hook: add diagnostic listing of chroot/boot/memtest* files

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

iso/builder/auto/config

@@ -30,8 +30,8 @@ lb config noauto \
     --linux-flavours "amd64" \
     --linux-packages "${LB_LINUX_PACKAGES}" \
     --memtest none \
-    --iso-volume "EASY-BEE" \
-    --iso-application "EASY-BEE" \
+    --iso-volume "EASY-BEE-${BEE_GPU_VENDOR_UPPER:-NVIDIA}" \
+    --iso-application "EASY-BEE-${BEE_GPU_VENDOR_UPPER:-NVIDIA}" \
     --bootappend-live "boot=live components video=1920x1080 console=tty0 console=ttyS0,115200n8 loglevel=7 username=bee user-fullname=Bee modprobe.blacklist=nouveau" \
     --apt-recommends false \
     --chroot-squashfs-compression-type zstd \