feat(correlation/attribution): wire bus handler, persist state (Phase 4)

attribution_worker.handle_observation_event now executes the full
end-to-end path:

* ensure stub identity (Phase 1)
* observations_for_identity_primitive() — new repo helper joining
  observations through attackers.identity_id, so v1's clusterer
  gets cross-attacker rollup for free
* aggregate_observations() with ValueKind dispatched off the BEHAVE
  PRIMITIVE_REGISTRY; unknown primitives default to categorical
* upsert_attribution_state() — last_change_ts locked when state is
  unchanged so the dashboard can render "stable since X"
* publish attribution.profile.state_changed only on transition;
  idempotent re-runs over the same observation set fire nothing
  (loop-prevention invariant matching ttp.tagged)

Tests:
* 5 end-to-end attribution scenarios over in-memory SQLite + FakeBus.
* test_base_repo's DummyRepo + coverage body now stub every abstract
  surface BaseRepository declares — the 6 added by this branch plus
  the 12 left un-stubbed by earlier work (BEHAVE Phase 1, TTP
  rollups, iter helpers). The coverage test could not previously
  even instantiate.
* test_aggregate_categorical's dispatcher rejection updated for the
  Phase 3 + 4 contract — ValueError on unknown kinds, not
  NotImplementedError.

decnet/web/db/repository.py

@@ -341,6 +341,20 @@ class BaseRepository(ABC):
         ordered by ``ts`` ASC. Empty list when none."""
         raise NotImplementedError
 
+    @abstractmethod
+    async def observations_for_identity_primitive(
+        self, identity_uuid: str, primitive: str,
+    ) -> list[dict[str, Any]]:
+        """Every observation of ``primitive`` across all attackers
+        rolling up to ``identity_uuid``, ordered by ``ts`` ASC.
+
+        Empty list when the identity has no observations of this
+        primitive. v0 with 1:1 stub identities returns the same set
+        as ``observations_time_series(attacker_uuid, primitive)``;
+        v1's clusterer makes the union meaningful.
+        """
+        raise NotImplementedError
+
     @abstractmethod
     async def has_observations_for_evidence(self, evidence_ref: str) -> bool:
         """True iff any observation row carries this ``evidence_ref``.