swarm: named scheduled prompts for one or more agents, fired in each agent

swarm-controller keeps every scheduled prompt (id, name, agents, body,
anchor, interval, paused) as one document under one key of a new
`schedule-definitions` KV bucket, so each change is a single
compare-and-set and a prompt exists for all of its agents or none. It
writes each agent's key of a new `agent-schedules` bucket as the prompts
naming that agent, without names or other agents, after every change and
on a one-minute reconcile pass. It is the only writer of both, behind
GET/POST /api/schedules and PATCH/DELETE /api/schedules/{id}.
`swarmctl schedule add|list|edit|pause|resume|rm` drives those routes over
the controller socket.

An agent's own queue credential is granted one more subject, the direct
get of its own key in `agent-schedules`. A KV watch is not granted: its
consumer create subject carries no key, so it would cover every agent's.

hive-agent's new schedule ticker reads that key every 10 seconds and fires
due slots as the same `schedule:<id>` todo hive-c0re's worker pushes. Fire
times are anchor + k*interval; the last fired slot per schedule id is kept
in the state db, so a body edit or list refresh never moves or refires a
slot, downtime fires the latest missed slot once, a restart refires
nothing, a one-shot fires once, and paused slots are skipped.

Refs #4914

nix/host-modules/swarm-nats.nix

@@ -850,6 +850,13 @@ in
                 # `term-sub-{agent}` stream that keeps them, so its subjects
                 # and limits are never the agent's to choose.
                 "--agent-token-publish-subject ${lib.escapeShellArg "\$\$SWARM.term.{agent}.sub.>"}"
+                # Reading its own key of the `agent-schedules` KV bucket
+                # (`swarm_queue_client::agent_schedules`), and nothing else of
+                # JetStream: a direct get names the key in its subject, so
+                # this one subject is one key. No `STREAM.INFO`, no
+                # `CONSUMER.CREATE` (a watch's create subject carries no key,
+                # so it would cover every agent's) and no `$KV` write.
+                "--agent-token-publish-subject ${lib.escapeShellArg "\$\$JS.API.DIRECT.GET.KV_agent-schedules.\$\$KV.agent-schedules.{agent}"}"
                 "--store-cert-role ${lib.escapeShellArg authCertRole}"
               ];
               # Every credential arrives by `LoadCredential` and is named