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/backups.html

@@ -72,6 +72,7 @@
   <div class="modal-dialog">
     <div class="modal-content">
       <form action="{{ url_for('clonezilla_upload') }}" method="post" enctype="multipart/form-data">
+        <input type="hidden" name="_csrf_token" value="{{ csrf_token() }}">
         <div class="modal-header">
           <h5 class="modal-title"><i class="bi bi-upload me-2"></i>Upload Backup</h5>
           <button type="button" class="btn-close" data-bs-dismiss="modal"></button>
@@ -100,6 +101,7 @@
   <div class="modal-dialog">
     <div class="modal-content">
       <form id="deleteForm" method="post">
+        <input type="hidden" name="_csrf_token" value="{{ csrf_token() }}">
         <div class="modal-header">
           <h5 class="modal-title"><i class="bi bi-exclamation-triangle me-2 text-danger"></i>Confirm Delete</h5>
           <button type="button" class="btn-close" data-bs-dismiss="modal"></button>