swarm-nats, matrix: the queue's and matrix-ctl's store identity paths are their own, not the hive's

glue-nats-bao-identity.nix and glue-matrix-ctl-bao-identity.nix defaulted
deploy.nats.baoClient{Cert,Key}File and deploy.matrix.ctlBaoClient{Cert,Key}File
to siblings of deploy.bao.clientCertFile, the hive's own store reader. That
pointed a store host whose reader was moved at files nobody mints, and on a
queue or homeserver host without the store that held a placed hive reader
invented a nats.pem / matrix-ctl.pem path beside it.

Both glues are now gated on the store running on this host
(deploy.bao.enable, the condition glue-bao-tls.nix mints under) and name the
directory the minting unit writes to, through nix/host-modules/lib/bao-pki-dir.nix.

Host shapes:
- Store host, default reader: unchanged. The evaluated paths stay
  /var/lib/swarm-bao-pki/nats{,-key}.pem and
  /var/lib/swarm-bao-pki/matrix-ctl{,-key}.pem, and the rendered units are
  the same.
- Store host whose hive reader was moved: now gets the leaf minted there.
- Queue or homeserver host without the store, holding a hive reader and not
  naming these options: no default any more. It still evaluates (neither
  option has an eval assertion). swarm-bao-nats-tls exits 1 naming
  deploy.nats.baoClient{Cert,Key}File when the queue's certificate is missing
  or due for renewal; swarm-bao-matrix-oidc exits 1 naming
  ctlBaoClient{Cert,Key}File, and the swarm appservice render/publish units
  and the PKI bind mount no longer render. If that host had placed nats.pem
  or matrix-ctl.pem beside its hive reader, it worked before and now needs
  both options named.
- Hosts without the store and without a hive reader, and hosts naming the
  options: unchanged.

Both refusals and option descriptions now say the default comes from
deploy.bao.enable.

Refs #4921

docs/integrations/matrix.md

@@ -143,6 +143,13 @@ A homeserver whose `swarm-matrix-ctl` has no store identity
 (`services.hyperhive.deploy.matrix.ctlBaoClientCertFile`) loads no
 registration, and nothing creates accounts on it.
 
+On the store's host `ctlBaoClientCertFile` / `ctlBaoClientKeyFile` default
+to the leaf `glue-bao-tls.nix` mints there. A homeserver host without the
+store gets no default, even when it holds the hive's own reader
+`deploy.bao.clientCertFile`: issue a leaf whose subject is
+`deploy.bao.matrixCtlCommonName`, place it, and name it in both options.
+Until you do, `swarm-bao-matrix-oidc` fails naming both.
+
 ### The swarm's appservice, and its admin sender
 
 The registration's id is `swarm`, its sender `@swarm`, and its user