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

hive-c0re/src/matrix.rs

@@ -58,13 +58,9 @@ const HTTP_TIMEOUT_SECS: u64 = 10;
 /// homeserver could not attribute an action to a hive and revoking one hive's
 /// standing revoked all of them.
 ///
-/// Also the `sender_localpart` of the hive's appservice registration,
-/// which is what creates this account on a homeserver that has never had
-/// one: the homeserver creates a registration's sender user itself, at
-/// startup, before it accepts a request. See
-/// `nix/host-modules/hive-matrix.nix`, where the same string is rendered as
-/// `hiveLocalpart`. **The two must match**; nothing wires an override
-/// across.
+/// `swarm-controller` creates this account with the swarm's appservice token
+/// (`matrix_account::hive_sender`) and stores its token where
+/// [`stored_sender_token`] reads it; hive-c0re never creates it.
 ///
 /// An ordinary account, with no homeserver-admin standing: what it
 /// provisions — the Space, the chat room, the invites — it provisions as