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/startnet_editor.html

@@ -52,6 +52,7 @@
       </div>
       <div class="card-body p-0">
         <form action="{{ url_for('startnet_save') }}" method="post" id="startnetForm">
+          <input type="hidden" name="_csrf_token" value="{{ csrf_token() }}">
           <textarea name="content" class="form-control cmd-editor" id="cmdEditor"
                     spellcheck="false">{{ content }}</textarea>
         </form>