matrix: swarm-controller is the only minter

Every hive is in a swarm and every swarm runs matrix, so every swarm has a
swarm-controller, and since #4810 its hive_sender pass mints each hive's
@hive-<hive>: sender token into the store every five minutes. The two
other minters of that token go:

- swarm-matrix-ctl mint: the systemd.services.swarm-matrix-ctl unit in the
  hive-matrix container, Command::Mint and src/mint.rs. The binary, its
  appservice render/publish verbs, ctlPackage, ctlActive and the ctl cert
  role stay. bao-matrix-reader's checks on the deleted unit are removed;
  the leaf-identity and no-token-in-env checks now look at
  swarm-matrix-appservice-publish, which runs under the same identity.
- the hive-side mint ladder in hive-c0re's ensure_hive_user
  (register/appservice-login/password-login with the local as_token), with
  read_appservice_token, paths::matrix_appservice_token and the helpers
  only it used. ensure_hive_user now takes the store's token, keeps the
  file when the store has none or can't be reached, and fails otherwise.
- hivectl matrix sync-admin: the verb, HostRequest::MatrixSyncAdmin and
  handle_matrix_sync_admin. The periodic MatrixSweep (ensure_all) is
  unchanged apart from no longer reading the local as_token.

This removes the double-mint race #4810's review flagged: two minters
logging in on one pinned device could leave a dead token in the store
until the next pass.

Closes #4813
Closes #4814

swarm-secret-client/src/matrix.rs

@@ -197,9 +197,9 @@ mod tests {
     #[test]
     fn the_localpart_is_derived_from_the_hive_name() {
         // The literal is the point: `nix/host-modules/hive-matrix.nix` renders
-        // the same string into the registration's `sender_localpart` and into
-        // `MATRIX_MINT_LOCALPART`, and nothing wires an override across — so a
-        // change here is a change there.
+        // the same string into the registration's `sender_localpart`, and
+        // nothing wires an override across — so a change here is a change
+        // there.
         assert_eq!(hive_localpart("pr1ma"), "hive-pr1ma");
         assert_ne!(
             hive_localpart("pr1ma"),