feat(iso): add nogpu variant (no NVIDIA, no AMD/ROCm)

- build.sh: accept --variant nogpu; skips all GPU build steps, removes
  both nvidia-cuda and rocm archives, strips bee-nvidia-load and
  bee-nvidia.service from overlay
- build-in-container.sh: add nogpu to --variant flag; all variant
  includes nogpu; --clean-build wipes live-build-work-nogpu
- 9000-bee-setup hook: nogpu path enables no GPU services
- bee-nogpu.list.chroot: empty GPU package list

Output: easy-bee-nogpu-vX.iso

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

iso/builder/build.sh

@@ -27,8 +27,8 @@ while [ $# -gt 0 ]; do
 done
 
 case "$BEE_GPU_VENDOR" in
-    nvidia|amd) ;;
-    *) echo "unknown variant: $BEE_GPU_VENDOR (expected nvidia or amd)" >&2; exit 1 ;;
+    nvidia|amd|nogpu) ;;
+    *) echo "unknown variant: $BEE_GPU_VENDOR (expected nvidia, amd, or nogpu)" >&2; exit 1 ;;
 esac
 
 BUILD_WORK_DIR="${DIST_DIR}/live-build-work-${BEE_GPU_VENDOR}"
@@ -249,8 +249,8 @@ rm -f \
     "${OVERLAY_STAGE_DIR}/usr/local/bin/bee-smoketest" \
     "${OVERLAY_STAGE_DIR}/usr/local/bin/all_reduce_perf"
 
-# Remove NVIDIA-specific overlay files for AMD variant
-if [ "$BEE_GPU_VENDOR" = "amd" ]; then
+# Remove NVIDIA-specific overlay files for non-nvidia variants
+if [ "$BEE_GPU_VENDOR" != "nvidia" ]; then
     rm -f "${OVERLAY_STAGE_DIR}/usr/local/bin/bee-nvidia-load"
     rm -f "${OVERLAY_STAGE_DIR}/etc/systemd/system/bee-nvidia.service"
 fi
@@ -387,9 +387,12 @@ CUBLAS_VERSION=${CUBLAS_VERSION}
 CUDA_USERSPACE_VERSION=${CUDA_USERSPACE_VERSION}
 NCCL_TESTS_VERSION=${NCCL_TESTS_VERSION}"
     GPU_BUILD_INFO="nvidia:${NVIDIA_DRIVER_VERSION}"
-else
+elif [ "$BEE_GPU_VENDOR" = "amd" ]; then
     GPU_VERSION_LINE="ROCM_VERSION=${ROCM_VERSION}"
     GPU_BUILD_INFO="rocm:${ROCM_VERSION}"
+else
+    GPU_VERSION_LINE=""
+    GPU_BUILD_INFO="nogpu"
 fi
 
 cat > "${OVERLAY_STAGE_DIR}/etc/bee-release" <<EOF
@@ -418,13 +421,19 @@ fi
 cp "${BUILD_WORK_DIR}/config/package-lists/bee-${BEE_GPU_VENDOR}.list.chroot" \
    "${BUILD_WORK_DIR}/config/package-lists/bee-gpu.list.chroot"
 
-# --- remove archives for the other vendor ---
+# --- remove archives for the other vendor(s) ---
 if [ "$BEE_GPU_VENDOR" = "nvidia" ]; then
     rm -f "${BUILD_WORK_DIR}/config/archives/rocm.list.chroot" \
           "${BUILD_WORK_DIR}/config/archives/rocm.key.chroot"
-else
+elif [ "$BEE_GPU_VENDOR" = "amd" ]; then
     rm -f "${BUILD_WORK_DIR}/config/archives/nvidia-cuda.list.chroot" \
           "${BUILD_WORK_DIR}/config/archives/nvidia-cuda.key.chroot"
+else
+    # nogpu: remove both
+    rm -f "${BUILD_WORK_DIR}/config/archives/rocm.list.chroot" \
+          "${BUILD_WORK_DIR}/config/archives/rocm.key.chroot" \
+          "${BUILD_WORK_DIR}/config/archives/nvidia-cuda.list.chroot" \
+          "${BUILD_WORK_DIR}/config/archives/nvidia-cuda.key.chroot"
 fi
 
 # --- substitute version placeholders in package list and archive ---
@@ -432,7 +441,7 @@ if [ "$BEE_GPU_VENDOR" = "nvidia" ]; then
     sed -i \
         -e "s/%%DCGM_VERSION%%/${DCGM_VERSION}/g" \
         "${BUILD_WORK_DIR}/config/package-lists/bee-gpu.list.chroot"
-else
+elif [ "$BEE_GPU_VENDOR" = "amd" ]; then
     sed -i \
         -e "s/%%ROCM_VERSION%%/${ROCM_VERSION}/g" \
         -e "s/%%ROCM_SMI_VERSION%%/${ROCM_SMI_VERSION}/g" \