docs: drop harness systemd settings; swarm-nats-auth: refuse the hive's shared agent client

Docs (review on #4948): the harness's restart settings are not useful to
a reader, so the `Restart`/`RestartSec` bullet in docs/turn-loop and the
"30 seconds later, no start limit" wording in docs/swarm are removed.
What stays is the behaviour: the harness exits and comes back until the
queue accepts it.

Grant: with the harness's shared-client fallback gone, nothing presents
the hive's shared agent client (`hive-<hive>-agent`) to the queue;
swarm-logs uses that OIDC client over HTTP only. swarm-nats-auth now
refuses it outright instead of granting the configured
`$SWARM.term.{hive}.>` / `$SWARM.agent-state.{hive}.>` publish and its
`_INBOX.client.<id>.>` subscribe, so an agent holding it can no longer
publish as a sibling. The agent arm still runs before the hive arm, so
that id never falls through to its hive's grant.

Removed with it: the `--agent-publish-subject` flag and its two uses in
swarm-nats.nix, `Policy`'s agent subject list, and
swarm-queue-client's `client_inbox_prefix`. The module-eval now asserts
the flag is absent; the policy tests assert the refusal and that the
hive itself is still admitted.

swarm-nats-auth/src/agent_token.rs

@@ -227,7 +227,6 @@ mod tests {
             "hive-status".to_owned(),
             vec!["swarm-controller".to_owned()],
             vec![],
-            vec!["$SWARM.term.{hive}.>".to_owned()],
         )
         .expect("valid")
         .with_agent_token_subjects(vec![
@@ -355,7 +354,6 @@ mod tests {
             "hive-status".to_owned(),
             vec![],
             vec![],
-            vec![],
         )
         .expect("valid");
         let Presented::Agent(token) = classify("swarm-agent.atlas.Ab9_-zSECRET") else {