build-usb: whole webapp, hard sfdisk failure, ISO-derived boot params, image-file mode; tests/vm harness

- Copy the whole webapp/ tree (minus __pycache__) in build-usb.sh and
  build-proxmox-iso.sh, so config, services/, views/ and
  blancco_evidence_monthly.py reach the server.
- sfdisk --append failure now aborts; the CIDATA partition is the one
  starting exactly at the computed sector, and nothing that starts
  before it is ever formatted (the old fallback hit the ISO's EFI
  partition).
- Volume id and El Torito load sizes come from the ISO
  (xorriso -report_el_torito as_mkisofs); grub.cfg must contain
  autoinstall after patching.
- --image FILE SIZE|auto builds the same layout in a file without root
  (mkfs.vfat -C + mtools, sfdisk on the file). Plus --payload-root,
  --skip-enrollment/-bios/-drivers/-boot-tools, --yes.
- tests/vm: libvirt harness (pxetest-server, pxetest-client, isolated
  pxetest-imaging network) with fetch-iso/build-image/create/start/
  status/stop/destroy.

tests/vm/build-image.sh

@@ -0,0 +1,57 @@
+#!/bin/bash
+# Build the installer USB as a disk image FILE with build-usb.sh image mode,
+# then upload it into the libvirt 'default' pool as volume pxetest-usb.img.
+#
+# Usage: tests/vm/build-image.sh [--with-enrollment] [--with-boot-tools] [--size SIZE]
+#   Default skips enrollment/, bios-staging/, drivers-staging/ and boot-tools/
+#   to keep the image small; SIZE defaults to "auto".
+# Env:   PXETEST_PAYLOAD_ROOT (where offline-packages/, boot-files/... live)
+source "$(dirname "$0")/common.sh"
+
+SIZE=auto
+SKIPS=(--skip-enrollment --skip-bios --skip-drivers --skip-boot-tools)
+while [ $# -gt 0 ]; do
+    case "$1" in
+        --with-enrollment) SKIPS=("${SKIPS[@]/--skip-enrollment}"); shift ;;
+        --with-boot-tools) SKIPS=("${SKIPS[@]/--skip-boot-tools}"); shift ;;
+        --size) SIZE="$2"; shift 2 ;;
+        *) die "unknown option $1" ;;
+    esac
+done
+ARGS=()
+for s in "${SKIPS[@]}"; do [ -n "$s" ] && ARGS+=("$s"); done
+
+[ -f "$UBUNTU_ISO" ] || die "no ISO at $UBUNTU_ISO; run tests/vm/fetch-iso.sh"
+ensure_image_tools
+
+# Report what the payload root has and lacks (do not invent content).
+log "payload root: $PXETEST_PAYLOAD_ROOT"
+for d in offline-packages pip-wheels boot-files boot-tools enrollment bios-staging drivers-staging; do
+    if [ -d "$PXETEST_PAYLOAD_ROOT/$d" ]; then
+        printf '    %-17s %s\n' "$d" "$(du -shL "$PXETEST_PAYLOAD_ROOT/$d" 2>/dev/null | cut -f1)"
+    else
+        printf '    %-17s MISSING\n' "$d"
+    fi
+done
+for f in ipxe-shimx64.efi ipxeboot.tar.gz wimboot boot.wim BCD boot.sdi bootx64.efi undionly.kpxe; do
+    [ -f "$PXETEST_PAYLOAD_ROOT/boot-files/$f" ] || log "    boot-files/$f MISSING"
+done
+
+if [ -e "$USB_IMAGE" ] && [ ! -f "$USB_IMAGE" ]; then
+    die "$USB_IMAGE is not a regular file"
+fi
+
+"$REPO_ROOT/scripts/build-usb.sh" --yes --payload-root "$PXETEST_PAYLOAD_ROOT" \
+    "${ARGS[@]}" --image "$USB_IMAGE" "$SIZE" "$UBUNTU_ISO"
+
+BYTES=$(stat -c%s "$USB_IMAGE")
+if dom_exists "$SERVER_VM" && [ "$(dom_state "$SERVER_VM")" != "shut off" ]; then
+    die "$SERVER_VM is running; stop it before replacing its USB volume"
+fi
+if vol_exists "$USB_VOL"; then
+    virsh vol-delete --pool "$POOL" "$USB_VOL" >/dev/null
+fi
+log "uploading $USB_IMAGE ($((BYTES / 1048576)) MiB) to pool $POOL as $USB_VOL"
+virsh vol-create-as "$POOL" "$USB_VOL" "$BYTES" --format raw >/dev/null
+virsh vol-upload --pool "$POOL" --sparse "$USB_VOL" "$USB_IMAGE"
+log "done"