docs(#3255): correct the rest of the relay-shaped wording

mara asked for the docs and comments to be fixed in one PR before the
implementation, since a half-corrected description is what confuses a
reader coming back after a context compact.

Three more places said or implied "forward the payload":

- post_webhook_forge's doc ("relays the delivery to every hive ... the
  payload is never parsed here")
- its OpenAPI request_body description ("the delivery can be relayed
  unmodified") -- this one is published in the spec, so it was the most
  externally visible of them
- DeliveryKind::as_str, which called the hook kind the event's routing
  key; the message is semantic, and which hook it arrived on is an input
  to deriving it rather than the thing sent

docs/swarm/README.md gains the direction next to the interim state, so
"two hooks, one of which only logs" reads as a step rather than a design.

docs/swarm/README.md

@@ -363,6 +363,13 @@ nothing more. **Do not delete either.** Removing a hive's hook stops that
 hive acting on knowledge pushes and config PRs; removing the
 controller's just gets recreated on its next start.
 
+Where this is going, so the interim state reads as interim: the
+controller will **interpret** a delivery and send hives a specific
+message — *the knowledge repo changed*, *deploy agent `foo` at rev
+`abc123`* — rather than forwarding forge payloads for each hive to
+re-derive. Approval happens once, at the swarm level, before the message
+is sent; a hive receives a decision, not an event to adjudicate.
+
 Nothing to configure. The hooks are registered only when this host also
 serves the swarm UI vhost — that is what publishes the endpoint, and a
 hook the forge cannot reach would collect failed deliveries while