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.

docs/swarm/schedules.md

@@ -78,8 +78,8 @@ or within a minute if the controller's first attempt to pass it on failed.
 
 - **The agent isn't connected to the swarm queue.** It reads its prompts with
   its own swarm-queue credential. A harness that can't connect retries for
-  about five minutes, then exits and restarts 30 seconds later; it reads no
-  prompts until a connect succeeds. See
+  about five minutes, then exits and comes back; it reads no prompts until a
+  connect succeeds. See
   [Giving the agents the queue too](README.md#giving-the-agents-the-queue-too).
 - **The agent hasn't read its prompts since it started.** It fires from the
   last list it read; until the first read succeeds it fires nothing. A read