Writing bao's `default` policy needed a new stanza in the granter's own
policy, which only the bootstrap token can upload, so deploying it took
a manual root-token step. Nothing needed it: the one reader of the
callout xkey's public half is `swarm-bao-nats-callout-xkey`, which logs
in as the `swarm-nats-auth` role, and that role's policy already names
the path. `swarm-bao-nats-auth-policy` writes that policy as the granter
on every deploy, under the granter's existing `sys/policies/acl/swarm-*`
grant.
Removed: the `swarm-bao-public-read-policy` unit, its marker block, the
granter's `sys/policies/acl/default` stanza, the granter-role restart of
that unit, the bao.md section and the module-eval cases pinning them.
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