Previously the reinstall endpoint required cached.template_id (clone-from-VM-
template flow), so LXC instances created via the wizard from an OS template
file (e.g. local:vztmpl/debian-13-...tar.zst) returned 'VM has no associated
template; reinstall is not available'.
Now reinstall works in two modes:
1) clone-from-template (existing): VM/LXC with cached.template_id pointing
to OSTemplate.vmid
2) ostemplate-file (new, LXC only): cached.template_name like
'storage:vztmpl/...tar.zst'. Reinstall stops, deletes, then re-creates
the container with the same VMID using create_lxc_container, preserving
network config, storage, rootfs size, swap, features, ssh_keys, etc.
pulled from the previous container config + VMInstance cache.
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