phase 2 (part 2): sqlc queries, audit/event helpers, event NOTIFY trigger

- sqlc.yaml + internal/db/queries/*.sql: typed queries for entities,
  relationships, ontology, operations (signals, events, audit,
  idempotency, entity_status)
- internal/db/sqlcgen/: generated Go from sqlc (pgx/v5)
- internal/observability/record.go: Audit() and Event() helpers that
  write in the caller's transaction (SG10). actorLabel is interim text
  identity in detail JSON until OIDC resolution lands; actor_id column
  exists but is not yet populated
- migrations/008: post-commit pg_notify trigger on events table for
  SSE fan-out (SG8/SG10)

internal/db/queries/relationships.sql

@@ -0,0 +1,33 @@
+-- name: ListEntityRelations :many
+SELECT se.slug AS source_slug, te.slug AS target_slug, r.type, r.attributes,
+       r.valid_from, r.valid_to
+FROM relationships r
+JOIN entities se ON se.id = r.source_id
+JOIN entities te ON te.id = r.target_id
+WHERE r.valid_to IS NULL
+  AND ((sqlc.arg('direction')::text IN ('out','both') AND r.source_id = sqlc.arg('id'))
+    OR (sqlc.arg('direction')::text IN ('in','both')  AND r.target_id = sqlc.arg('id')))
+  AND (sqlc.narg('rel_type')::text IS NULL OR r.type = sqlc.narg('rel_type'))
+ORDER BY r.type, se.slug, te.slug;
+
+-- name: ListGraphEdges :many
+SELECT se.slug AS source_slug, te.slug AS target_slug, r.type, r.attributes,
+       r.valid_from, r.valid_to
+FROM relationships r
+JOIN entities se ON se.id = r.source_id
+JOIN entities te ON te.id = r.target_id
+WHERE r.valid_to IS NULL
+  AND r.source_id = ANY(sqlc.arg('ids')::uuid[])
+  AND r.target_id = ANY(sqlc.arg('ids')::uuid[])
+  AND (sqlc.narg('rel_types')::text[] IS NULL OR r.type = ANY(sqlc.narg('rel_types')::text[]))
+ORDER BY r.type, se.slug, te.slug;
+
+-- name: UpsertCurrentRelationship :exec
+INSERT INTO relationships (source_id, target_id, type, attributes, valid_from, valid_to)
+VALUES ($1, $2, $3, $4, now(), NULL)
+ON CONFLICT (source_id, target_id, type) WHERE valid_to IS NULL
+DO UPDATE SET attributes = EXCLUDED.attributes;
+
+-- name: EndCurrentRelationship :execrows
+UPDATE relationships SET valid_to = now()
+WHERE source_id = $1 AND target_id = $2 AND type = $3 AND valid_to IS NULL;