install: stage pxe-setup.sh at /usr/local/sbin/vetting-pxe-setup

proxmox-install.sh tarball-extracts into a tempdir that gets wiped on
EXIT, so after the one-liner there's no pxe-setup.sh on disk for the
operator to run. Have install.sh drop the script + ipxe-shas.txt into
/usr/local/share/vetting/ and symlink it as
/usr/local/sbin/vetting-pxe-setup (in PATH).

pxe-setup.sh now readlink -f's BASH_SOURCE so the symlink resolves to
the share dir where ipxe-shas.txt lives, and gracefully handles the
case where install.sh already staged vmlinuz + initrd.img into
LIVE_DIR (no bundle live-image/ needed at that point).

Update the trailing hint in proxmox-install.sh and the operations
runbook to surface the new `sudo vetting-pxe-setup ...` command.

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

deploy/proxmox-install.sh

@@ -78,7 +78,12 @@ To pin a specific build:
         ${REGISTRY_URL}/${PACKAGE_OWNER}/Vetting/raw/branch/main/deploy/proxmox-install.sh \\
         | sudo bash
 
-For PXE support, the bundle also ships deploy/pxe-setup.sh — see
-docs/operations.md for the flow.
+For PXE support, run:
+    sudo vetting-pxe-setup \\
+        --interface eth0 \\
+        --subnet 192.168.1.0/24 \\
+        --orchestrator-url http://<lxc-lan-ip>:8080
+
+See docs/operations.md for the full flow.
 
 EOF