hive: stop controlling the swarm's forge and matrix containers

The forge and matrix are swarm services; per mara's ruling on #5475
(shape a) a hive no longer starts, stops or restarts them.

- hive-priv-sock: InfraContainer keeps only Gateway; InfraTarget goes,
  service_unit maps the gateway to nginx.service directly. A
  ControlInfraContainer naming Forge/Matrix fails to decode.
- hive-host-sock: LifecycleScope drops forge/matrix and refuses unknown
  fields, so an older hivectl's --forge is an error rather than an
  all-false scope meaning everything.
- hive-c0re: scoped_infra selects only the gateway.
- hivectl: --forge/--matrix removed from stop/start/restart.
- docs: services.md says how the forge and matrix are managed;
  security.md, coordinator.md and hivectl-cli.md follow.
- hive-host-sock, hivectl/power.rs: Stop and RestartScoped doc comments name the gateway (host nginx.service), not infra containers.

hivectl/src/subvol.rs

@@ -16,9 +16,7 @@ fn single_agent_scope(name: &str) -> hive_host_sock::LifecycleScope {
     hive_host_sock::LifecycleScope {
         agents: false,
         agent_names: vec![name.to_owned()],
-        forge: false,
         gateway: false,
-        matrix: false,
     }
 }