* fix(debian-13-vm): disable systemd-firstboot and add autologin via virt-customize
Newer Debian 13 (Trixie) nocloud images (Jan 29+) have systemd-firstboot
enabled, which blocks the boot process by prompting for timezone and root
password on the serial console. The noVNC console stalls after auditd checks.
Fix by using virt-customize (like docker-vm.sh) to:
- Disable systemd-firstboot.service and mask it
- Pre-seed timezone to Etc/UTC
- Configure autologin on ttyS0 and tty1 for nocloud images
- Set hostname and clear machine-id for unique IDs
- Install libguestfs-tools if not present
Fixes#11807
* feat(debian-13-vm): add cloud-init selection dialog for default and advanced settings
Add select_cloud_init() function consistent with docker-vm.sh that prompts
the user to choose between Cloud-Init (genericcloud image) and nocloud
(with auto-login) in both default and advanced settings.
Previously, default settings hardcoded CLOUD_INIT=no without asking.
