feat: build NVIDIA open kernel modules during ISO build

- build-nvidia-module.sh: downloads nvidia open-gpu-kernel-modules source,
  builds against linux-lts headers, extracts nvidia-smi from .run installer
- modules cached by driver version + kernel version (rebuild only on update)
- .ko files injected into ISO overlay at /lib/modules/<kver>/extra/nvidia/
- bee-nvidia init script loads nvidia/nvidia-modeset/nvidia-uvm at boot
- NVIDIA_DRIVER_VERSION=550.54.15 (Turing+, H100/A100 supported)

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

iso/builder/genapkovl-bee_debug.sh

@@ -67,6 +67,7 @@ rc_add savecache shutdown
 rc_add bee-sshsetup default
 rc_add bee-network default
 rc_add dropbear default
+rc_add bee-nvidia default
 rc_add bee-audit-debug default
 
 if [ -d "$OVERLAY/etc" ]; then cp -r "$OVERLAY/etc/." "$tmp/etc/"; fi