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/clustering/campaign/factory.py

@@ -0,0 +1,31 @@
+"""Campaign-clusterer factory.
+
+Mirrors :mod:`decnet.clustering.factory` for the campaign layer.
+Configuration knob ``DECNET_CAMPAIGN_CLUSTERER_TYPE``; default
+``"connected_components"``.
+"""
+from __future__ import annotations
+
+import os
+
+from decnet.clustering.campaign.base import CampaignClusterer
+
+_KNOWN: tuple[str, ...] = ("connected_components",)
+_DEFAULT = "connected_components"
+
+
+def get_campaign_clusterer() -> CampaignClusterer:
+    name = os.environ.get(
+        "DECNET_CAMPAIGN_CLUSTERER_TYPE", _DEFAULT,
+    ).strip().lower()
+    if name == "connected_components":
+        from decnet.clustering.campaign.impl.connected_components import (
+            ConnectedComponentsCampaignClusterer,
+        )
+        return ConnectedComponentsCampaignClusterer()
+    raise ValueError(
+        f"Unknown campaign clusterer: {name!r}. Known: {_KNOWN}"
+    )
+
+
+__all__ = ["get_campaign_clusterer"]