migrate ISO build from Alpine to Debian 12 (Bookworm)

Replace the entire live CD build pipeline:
- Alpine SDK + mkimage + genapkovl → Debian live-build (lb config/build)
- OpenRC init scripts → systemd service units
- dropbear → openssh-server (native to Debian live)
- udhcpc → dhclient for DHCP
- apk → apt-get in setup-builder.sh and build-nvidia-module.sh
- Add auto/config (lb config options) and auto/build wrapper
- Add config/package-lists/bee.list.chroot replacing Alpine apks
- Add config/hooks/normal/9000-bee-setup.hook.chroot to enable services
- Add bee-nvidia-load and bee-sshsetup helper scripts
- Keep NVIDIA pre-compile pipeline (Option B): compile on builder VM against
  pinned Debian kernel headers (DEBIAN_KERNEL_ABI), inject .ko into includes.chroot
- Fixes: native glibc (no gcompat shims), proper udev, writable /lib/modules,
  no Alpine modloop read-only constraint, no stale apk cache issues

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

iso/builder/VERSIONS

@@ -1,4 +1,5 @@
-ALPINE_VERSION=3.21
+DEBIAN_VERSION=12
+DEBIAN_KERNEL_ABI=6.1.0-28
 NVIDIA_DRIVER_VERSION=590.48.01
 GO_VERSION=1.23.6
 AUDIT_VERSION=0.1.0