The management binary is embedded by downstream builds that override
server construction via SetNewServer, but the cobra command tree itself
was closed: rootCmd is unexported and fully assembled in init, with no
way to attach additional subcommands. Customize hands the built root
command to a caller-supplied function before Execute, so an embedding
binary can add its own commands next to — or under — the built-in ones,
such as extra administrative helpers beneath the existing admin group.
