Add Proxmox ISO builder, CSRF protection, boot-files integration

- Add build-proxmox-iso.sh: remaster Ubuntu ISO with autoinstall config,
  offline packages, playbook, webapp, and boot files for zero-touch
  Proxmox VM deployment
- Add boot-files/ directory for WinPE boot files (wimboot, boot.wim,
  BCD, ipxe.efi, etc.) sourced from WestJeff playbook
- Update build-usb.sh and test-vm.sh to bundle boot-files automatically
- Add usb_root variable to playbook, fix all file copy paths to use it
- Unify Apache VirtualHost config (merge default site + webapp proxy)
- Add CSRF token protection to all webapp POST forms and API endpoints
- Update README with Proxmox deployment instructions

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

webapp/templates/import.html

@@ -13,6 +13,7 @@
       <div class="card-body">
         {% if usb_mounts %}
         <form method="POST" id="importForm">
+          <input type="hidden" name="_csrf_token" value="{{ csrf_token() }}">
           <div class="mb-3">
             <label for="source" class="form-label fw-semibold">Source (USB Mount Point)</label>
             <select class="form-select" name="source" id="source" required>