Add ova2vzdump: OVA -> Proxmox vzdump (.vma.zst) converter

Dockerized converter that turns VirtualBox/VMware OVA appliances into
native Proxmox vzdump backups restorable via qmrestore, without needing
a PVE host.

- OVF parser (CPU/RAM/disks/NICs, SCSI/SATA/IDE controllers)
- Streaming OVA extractor
- qemu-server.conf generator with required #qmdump#map lines
- Orchestrator: qemu-img convert -> vma create -> zstd
- Click CLI: convert, create-test-ova, gui subcommands
- Flask web UI with Convert + Create-test-OVA tabs, SSE progress
- Dockerfile: Debian bookworm + pve-no-subscription for vma/qemu-img,
  pre-caches Alpine tiny raw image (sha512-verified) for bootable
  test-OVA generation
- End-to-end verified: generated OVA imports into VirtualBox, converted
  vzdump restores on Proxmox and the VM boots

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

.dockerignore

@@ -0,0 +1,10 @@
+.git
+.gitignore
+__pycache__
+*.pyc
+*.egg-info
+.venv
+venv
+.pytest_cache
+.mypy_cache
+data