test(clustering): fixture 2 vpn_hopping + fingerprint/asn references

One campaign, one DSL actor, ip_pool: rotating + rotation_count: 5
across 5 synthetic private-use ASNs (RFC 6996 64512-64516). Stable
JA3, HASSH, and payload_hash across every rotation — these are the
"signals the attacker can't cheaply rotate" per IDENTITY_RESOLUTION.md
and the load-bearing reason all 5 observation rows must resolve to
one identity / one campaign.

Two new reference clusterers in fixture_harness.py:

* fingerprint_clusterer — groups by (ja3, hassh). Un-fingerprinted
  rows stay singleton so it doesn't trivially fuse all noise into one
  mega-cluster. Approximates the stable-signal arm of the planned
  similarity graph.

* asn_clusterer — deliberately-bad reference for fixture 2's
  adversarial test. Group-by-ASN shatters the campaign into 5
  singletons; completeness collapses to 0.

Four tests in test_vpn_hopping_fixture.py: corpus shape (5 rows, 1
identity, 1 campaign, 5 distinct ASNs/IPs, stable fingerprints),
pass at campaign level, pass at identity level (asserts ARI exactly
1.0), asn_clusterer breaches the completeness floor.

tests/fixtures/campaigns/vpn_hopping.expected.yaml

@@ -0,0 +1,25 @@
+# Bounds for fixture 2 (vpn_hopping).
+#
+# Ground truth at campaign-level: 1 campaign of 5 observation rows.
+# Ground truth at identity-level: 1 identity of 5 observation rows.
+# A correct algorithm scores 1.0 across every metric on this fixture.
+#
+# Completeness is the load-bearing metric: a clusterer that fragments
+# the campaign by IP/ASN tanks completeness (the one true class is
+# split across many predicted clusters). The adversarial asn_clusterer
+# in the test file demonstrates this and the bound below rejects it.
+#
+# No true singletons in this fixture — singleton_recall is trivially
+# 1.0 (the metric returns 1.0 when truth has no singletons).
+#
+# Bounds are loose at v1; tighten as the algorithm matures. Loosening
+# any bound to make CI pass requires PR-comment justification (per
+# CAMPAIGN_CLUSTERING.md §2).
+adjusted_rand_index:
+  min: 0.85
+homogeneity:
+  min: 0.90
+completeness:
+  min: 0.80
+singleton_recall:
+  min: 0.95