Blancco PXE boot via Ubuntu kernel switch_root

Blancco's own kernel freezes on Dell Precision towers during PXE boot.
Workaround: boot Ubuntu kernel via GRUB chainload, download Blancco's
666MB squashfs rootfs + 132MB kernel modules over HTTP, mount overlay
filesystem, and switch_root into Blancco's userspace.

- Add blancco-init.sh: custom initramfs init script for switch_root approach
- Add blancco-preferences.xml: pre-configured with network share for reports
- Update playbook: build initramfs, deploy Ubuntu kernel/modules, config
- Update prepare-boot-tools.sh: add HTTP modules to GRUB EFI build
- Add UEFI HTTP Boot support to dnsmasq config
- iPXE menu chains to grubx64.efi (replaces sanboot of ISO)

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

prepare-boot-tools.sh

@@ -248,7 +248,7 @@ PYEOF
                 grub-mkstandalone \
                     --format=x86_64-efi \
                     --output="$OUT_DIR/blancco/grubx64.efi" \
-                    --modules="linux normal echo net efinet tftp chain sleep" \
+                    --modules="linux normal echo net efinet http tftp chain sleep all_video efi_gop" \
                     "boot/grub/grub.cfg=$GRUB_CFG" 2>/dev/null
                 echo "    Built grubx64.efi ($(du -h "$OUT_DIR/blancco/grubx64.efi" | cut -f1))"
             else