matrix: drop the per-hive appservice and its unused token

Every hive's homeserver loaded a per-hive `hyperhive` appservice
registration, and the swarm minted and delivered an as_token for it
through bao. No client presented that token: swarm-controller creates
every `@hive-<hive>` sender and every agent account with the swarm
appservice token (hive_sender.rs, agent_token.rs), and no Rust code read
the per-hive one.

Removed, with everything that existed only to serve it:
- hive-matrix.nix: the `hyperhive` registration, its activation-time
  render, the host bind mount of /var/lib/hyperhive/matrix-appservice,
  its LoadCredential entry, and the internal options
  `deploy.matrix.appserviceTokenFile` / `appserviceRegistrationScript`.
  tuwunel now loads only the swarm registration.
- glue-matrix-bao-token.nix and its `swarm-bao-matrix-token` unit.
- glue-bao-tls.nix: the matrix-token leaf and its defaults.
- swarm-bao.nix: the `swarm-matrix-token-<hive>` roles and policies
  (`swarm-bao-matrix-token-policy`), and the options
  `deploy.bao.matrixTokenClient{Cert,Key}File` and
  `matrixTokenCommonNamePrefix`, now mkRemovedOptionModule.
- swarm-secret-publisher.nix: the per-hive token mint and its state dir.
- swarm.nix: the reserved `<matrixTokenCommonNamePrefix>-<hive>` CN.
- swarm-secret-client: `matrix::appservice_token_path`.

The swarm registration (swarm-matrix-ctl, swarm-controller) is untouched.
Comments and docs that pointed at the removed glue file now point at
glue-queue-agent-credential.nix, which has the same reader shape.

Refs #4428

nix/host-modules/hive-c0re/default.nix

@@ -333,8 +333,8 @@ in
           # reachable from an unprivileged daemon without widening either.
           # The gate is the identity, never `deploy.bao.enable`: a hive that
           # reads a store on another machine holds one of these and runs no
-          # store. ./glue-matrix-bao-token.nix gates its own reader the same
-          # way.
+          # store. ./glue-queue-agent-credential.nix gates its own reader the
+          # same way.
           ++ lib.optionals baoClientIdentity [
             "bao-client.pem:${baoDeploy.clientCertFile}"
             "bao-client-key.pem:${baoDeploy.clientKeyFile}"

nix/host-modules/hive-c0re/environment.nix

@@ -11,7 +11,7 @@ let
   cfg = config.services.hyperhive.c0re;
   baoDeploy = config.services.hyperhive.deploy.bao;
   baoCfg = config.services.hyperhive.swarm.bao;
-  # The same test ../glue-matrix-bao-token.nix applies, and for the same
+  # The same test ../glue-queue-agent-credential.nix applies, and for the same
   # reason: a reader is defined by holding a certificate the store accepts,
   # not by sharing a host with the store. Deriving this from
   # `deploy.bao.enable` would be the co-location assumption itself.