dotfiles: install VirtualBox with the other winget packages

dotfiles: install VirtualBox with the other winget packages

The test VMs this box drives are VirtualBox ones -- it is why sshd's firewall
rule is widened to every profile, a host-only or bridged adapter being routinely
classified Public -- so the hypervisor belongs in the same list as everything
else the box is provisioned with, rather than being the one install left to do
by hand.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01D4ozcQcqMSJBi2Ez4Pfxyc