feat: metrics record --emit-event for kaizen.metrics.recorded

Publish activity-core EventEnvelope payloads to NATS subject
activity.kaizen.metrics.recorded after a successful append.
Optional nats-py via kaizen-agentic[events]; project slug from
KAIZEN_PROJECT_SLUG or directory basename. Skips emit on
idempotency duplicates. Closes KAIZEN-WP-0008 T03.

src/kaizen_agentic/integrations/__init__.py

@@ -1,10 +1,18 @@
-"""Ecosystem integration adapters (Helix Forge, artifact-store)."""
+"""Ecosystem integration adapters (Helix Forge, artifact-store, event bus)."""
 
 from .artifact_store import publish_optimizer_evidence
+from .event_bus import (
+    build_metrics_recorded_envelope,
+    publish_metrics_recorded_event,
+    resolve_project_slug,
+)
 from .helix import HelixCorrelationAdapter, enrich_helix_correlation
 
 __all__ = [
     "HelixCorrelationAdapter",
+    "build_metrics_recorded_envelope",
     "enrich_helix_correlation",
+    "publish_metrics_recorded_event",
     "publish_optimizer_evidence",
+    "resolve_project_slug",
 ]