Instance names now equal the box name (claudebox new --name work -> 'work',
not 'claude-work'). To still tell claudebox's instances apart from any other
incus instances, tag each on creation with user.claudebox=1 and filter status
+ teardown by that tag instead of a name prefix. Clones (new --from) inherit
the tag.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>