The schema's event fields gain values, a values_from marker (agents, repos)
and a closed flag; a node field gains the marker and the flag. kind is now
listed as issue and PR, what the router sends. The flow editor shows a
dropdown where the list is complete, suggestions where it is only examples,
and a plain box where there is none.
The router gets a request_reviewer node and a pull_request_sync source;
the built-in head-classifier flow asks swarm-controller, over
$SWARM.router.sink.request-reviewer, to request review-classifier on
every push, unless its review of the head already stands. The controller
subscribes to pull_request_sync on its pull-request hook and answers
the router; nats-auth grants the router the publish and the controller
the subscribe.
