swarm-matrix-ctl: mint the swarm's own appservice registration

The swarm gets an appservice identity of its own, separate from each hive's
`hyperhive` registration. `swarm-matrix-ctl appservice render` mints its
tokens inside the matrix container when they are absent and renders the
registration tuwunel loads; `appservice publish` writes its as_token to
`swarm/controller/swarm-controller/matrix/appservice-token`, the one kind no
hive's policy grants.

The homeserver calls move out of swarm-matrix-ctl into swarm-matrix-client,
with a `whoami`, so swarm-controller can mint agents' accounts through the
same pinned device id instead of a copy of them.

swarm-matrix-ctl/src/mint.rs

@@ -21,7 +21,9 @@ use swarm_secret_client::{
     matrix,
 };
 
-use crate::{homeserver, registration};
+use swarm_matrix_client as homeserver;
+
+use crate::registration;
 
 /// Role on the store's `cert` auth mount to log in with. Its policy is what
 /// allows the write below; the certificate the `BAO_*` variables name has to