Revert all Blancco changes from this session

User reports Blancco was working before our mirror/session activity
today - then my attempted fixes (grubx64.efi rebuild, kexec-initrd
driver sweep, verbose blancco-init.sh) made it worse:

  - First attempt (narrow igc driver add) did not help because the
    switch-root path was not the one actually loaded by grubx64.efi's
    embedded config.
  - Second attempt (swapped grub embedded config to Ubuntu-kernel path)
    got further, but then kexec-initrd modules failed on insmod.
  - Third attempt (full ethernet tree sweep) pulled in broken ancient
    drivers (winbond-840, w5100-spi, xirc2ps_cs) that failed with
    unknown-symbol errors and prevented good drivers from loading.

Full revert: .gitignore, blancco-init.sh, pxe_server_setup.yml back to
the pre-session commit 6dcf832 state. Removes boot-tools/blancco/grub-
blancco.cfg from git (it was only added this session).

Runtime on both PXE servers was also restored: grubx64.efi and
kexec-initrd.img reverted from the .bak files taken before each
modification this session.

Whatever was there before today is now restored byte-for-byte on both
servers. If there is still a Blancco boot issue on specific modern
hardware that the user needs to fix, we will diagnose that narrowly
against the actual failure mode on that specific machine, not by
making sweeping preemptive changes.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

boot-tools/blancco/grub-blancco.cfg

@@ -1,31 +0,0 @@
-set default=0
-set timeout=0
-set gfxpayload=text
-
-insmod all_video
-insmod efi_gop
-insmod efinet
-insmod net
-insmod http
-net_bootp efinet0
-net_bootp efinet1
-net_bootp efinet2
-net_bootp efinet3
-
-# Boot Ubuntu kernel + small custom initramfs (kexec-initrd.img).
-# The custom init brings up the NIC (drivers baked in at build time:
-# e1000e, igb, igc, bnxt_en, tg3, bnx2, b44, r8169, atlantic, ...
-# much broader than Blancco's native vmlinuz-bde-linux ships with),
-# HTTP-fetches the Blancco rootfs (airootfs.sfs + native kernel +
-# initramfs) from this PXE server, overlay-mounts the rootfs, then
-# kexecs into Blancco's environment.
-#
-# Previous native-kernel path (linux ...vmlinuz-bde-linux via TFTP)
-# was abandoned because Blancco's kernel ships with a narrow NIC
-# driver set that fails on modern Dell Latitude 5330/5440 and
-# newer 'Pro' series with Intel I225/I226 NICs - "no network card
-# found" at the Blancco UI after TFTP load succeeds.
-menuentry "Blancco Drive Eraser" {
-    linux (http,10.9.100.1)/blancco/vmlinuz-ubuntu ip=dhcp
-    initrd (http,10.9.100.1)/blancco/kexec-initrd.img
-}