feat(clustering): campaign-clusterer worker + bus topics + CLI

The campaign clusterer worker mirrors the identity-side worker shell
(bus connect, heartbeat, control listener, slow-tick fallback) but
wakes on identity.> instead of attacker.> — campaign-level work is
gated on identity-layer changes, not raw observations.

The connected-components implementation reads identities via
list_identities_for_clustering, projects them with from_identity_row,
runs union-find over combined_campaign_weight, writes campaigns rows,
sets attacker_identities.campaign_id, and runs the same revocable-
merge pass as the identity layer (a merged-out campaign whose
identities no longer co-cluster with the winner gets revoked).

Bus: adds campaign.> family (formed / identity.assigned / merged /
unmerged) plus the cross-family identity.campaign.assigned so
existing identity-stream subscribers see the badge update without
having to subscribe to campaign.>. Wiki Service-Bus.md updated in
wiki-checkout in the same wave per the project's bus-signals
discipline.

CLI: decnet campaign-clusterer registered as master-only via
MASTER_ONLY_COMMANDS; --poll-interval / --daemon mirror the identity
clusterer command surface.

decnet/cli/gating.py

@@ -29,7 +29,7 @@ MASTER_ONLY_COMMANDS: frozenset[str] = frozenset({
     "api", "swarmctl", "deploy", "redeploy", "teardown",
     "mutate", "listener", "profiler",
     "services", "distros", "correlate", "archetypes", "web",
-    "db-reset", "init", "webhook", "clusterer",
+    "db-reset", "init", "webhook", "clusterer", "campaign-clusterer",
 })
 MASTER_ONLY_GROUPS: frozenset[str] = frozenset({"swarm", "topology", "geoip"})