Automate PXE setup: release bundle + pxe-setup.sh + startup validation

Collapses the LXC side of PXE enablement from a six-step manual dance
(build, fetch iPXE, scp, bridge, hand-edit yaml) into:

  make release                   # dev box (Linux/WSL)
  scp bundle.tar.gz lxc:/tmp/
  sudo ./install.sh              # base install, unchanged
  sudo ./pxe-setup.sh --interface ... --dhcp-range ... --orchestrator-url ...

pxe-setup.sh fetches iPXE from boot.ipxe.org, verifies against pinned
SHA256s in deploy/ipxe-shas.txt (fail-closed), places vmlinuz/initrd.img
from the bundle, and rewrites only the pxe: block of vetting.yaml.
Idempotent; --force gates overwriting a hand-edited block.

Adds Supervisor.Validate() — called before dnsmasq spawn — so typo'd
configs fail at orchestrator startup with clear errors naming the
missing file or yaml key, instead of silently serving broken TFTP
until a real host tries to PXE-boot. Nine tests cover missing files,
bogus interface, malformed dhcp_range, bad orchestrator_url, and
aggregate reporting.

Hypervisor bridge creation stays documented (LXC can't do it) but
everything downstream of the bridge is now scripted.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

cmd/vetting/main.go

@@ -149,6 +149,7 @@ func main() {
 			OrchestratorURL: cfg.PXE.OrchestratorURL,
 			RuntimeDir:      filepath.Join(cfg.Logs.Dir, "..", "pxe"),
 			TFTPRoot:        tftpRoot,
+			LiveDir:         cfg.PXE.LiveDir,
 		})
 	}