feat(hive-c0re): offer this hive's readiness to the swarm

The controller reads per-hive status out of a JetStream KV bucket and
nothing was writing one, so every hive rendered `never_reported`. This is
the half that makes the read path mean anything.

A hive offers; the controller never reaches down to collect. The gateway
has gone down in a way where every recovery channel ran through the one
broken thing, so a status path that depended on the controller would go
dark exactly when it is needed to diagnose the controller's own network.

What it publishes is what the hive already says about itself —
`warnings::readiness()`, the same value `/health/ready` serves. Nothing
here stamps a time: freshness is derived by the reader from when the value
landed, so a hive cannot make itself look fresher than it is, and a hive
with a wrong clock skews only its own payload.

The key is this hive's `hiveName`, which `swarm.nix` already asserts is a
key of `swarm.hives` — so a hive that evaluates at all publishes under a
name the roster knows, rather than by convention.

Publish first, then wait: a hive that has just come up is the one whose
status someone is looking at, and sleeping first would make every restart
read stale for a full interval. The interval is one decision with the
controller's staleness threshold, not two — a ratio of 2 means one lost
publish still reads fresh and two consecutive misses read stale.

Failures go to the dashboard banner through SweepHealth, debounced, at
`warn` and deliberately not `crit`: `crit` is what makes this hive report
itself degraded, and a hive that cannot reach the queue is not unhealthy —
the swarm's view of it is. Publishing `degraded` because the publish
failed would be both false and self-erasing on the next tick.

Cargo.lock

@@ -1664,6 +1664,7 @@ name = "hive-c0re"
 version = "0.1.0"
 dependencies = [
  "anyhow",
+ "async-nats",
  "axum",
  "base64",
  "bcrypt",
@@ -1695,6 +1696,7 @@ dependencies = [
  "serde",
  "serde_json",
  "sha2 0.11.0",
+ "swarm-queue-client",
  "tempfile",
  "tokio",
  "tokio-stream",