ova: fix packer validate errors; add KVM qcow2 artifact output

- Update ISO to ubuntu-24.04.4, hardcode SHA256 checksum (24.04.2 removed from mirrors)
- Remove headless variable (not declared in QEMU-only HCL, QEMU is always headless)
- Add qcow2-to-kvm.sh post-processor for KVM/libvirt/Proxmox deployments
- Add qcow2-to-ova.sh (converts qcow2 → stream-optimized VMDK → OVA without ovftool)
- packer validate now passes cleanly

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

zroc-ova/scripts/qcow2-to-kvm.sh

@@ -0,0 +1,50 @@
+#!/usr/bin/env bash
+# qcow2-to-kvm.sh — Package a QEMU qcow2 image as a KVM/libvirt/Proxmox artifact.
+#
+# Usage: qcow2-to-kvm.sh <qemu_output_dir/vm_name> <output.qcow2>
+#
+# Example:
+#   qcow2-to-kvm.sh ../output/qemu/zroc-appliance-1.0.0 \
+#                   ../output/zroc-appliance-1.0.0-ubuntu-24.04-amd64.qcow2
+
+set -euo pipefail
+
+QEMU_VM_PATH="$1"   # path to qcow2 (without extension) or directory
+QCOW2_OUT="$2"      # destination .qcow2 file
+
+# ── Locate the source qcow2 ───────────────────────────────────────────────────
+if [[ -f "${QEMU_VM_PATH}.qcow2" ]]; then
+  QCOW2_SRC="${QEMU_VM_PATH}.qcow2"
+elif [[ -d "$QEMU_VM_PATH" ]]; then
+  QCOW2_SRC=$(find "$QEMU_VM_PATH" -name "*.qcow2" | head -1)
+else
+  QCOW2_SRC="$QEMU_VM_PATH"
+fi
+
+if [[ -z "$QCOW2_SRC" || ! -f "$QCOW2_SRC" ]]; then
+  echo "ERROR: could not find qcow2 image at ${QEMU_VM_PATH}" >&2
+  exit 1
+fi
+
+echo "==> [qcow2-to-kvm] Source qcow2: $QCOW2_SRC"
+echo "==> [qcow2-to-kvm] Output qcow2: $QCOW2_OUT"
+
+mkdir -p "$(dirname "$QCOW2_OUT")"
+
+# Re-encode with qemu-img to compact/sparsify and ensure compatibility.
+# subformat=compressed produces a space-efficient image suitable for distribution.
+echo "==> [qcow2-to-kvm] Compacting qcow2 for distribution…"
+qemu-img convert \
+  -f qcow2 \
+  -O qcow2 \
+  -o compression_type=zlib,preallocation=off \
+  "$QCOW2_SRC" \
+  "$QCOW2_OUT"
+
+SIZE=$(du -sh "$QCOW2_OUT" | cut -f1)
+SHA=$(sha256sum "$QCOW2_OUT" | awk '{print $1}')
+
+echo "==> [qcow2-to-kvm] qcow2 complete: $QCOW2_OUT ($SIZE)"
+echo "==> [qcow2-to-kvm] SHA256: $SHA"
+echo "$SHA  $(basename "$QCOW2_OUT")" > "${QCOW2_OUT}.sha256"
+echo "==> [qcow2-to-kvm] Done"