fix(#3396): name the matrix bundle from a literal, not a missing option

hive-matrix.nix declares no `machine` option -- the idiom was copied from
swarm-grafana, which does. Any hive with matrix enabled failed to evaluate.

nix/host-modules/hive-matrix.nix

@@ -798,9 +798,12 @@ in
             # so naming the hive anchor alone would drop every public CA and
             # break federation with the wider matrix network — trading a small
             # outage for a much larger one.
+            # A literal, not an option: this module names its container
+            # `containers.hive-matrix` directly and declares no `machine`
+            # option to derive it from.
             (caTrust.trustBundle {
               inherit pkgs;
-              name = cfg.machine;
+              name = "hive-matrix";
               consumers = [ "tuwunel" ];
             })
           ];