list_registry

List the canonical shared entities in the portfolio registry. Each row carries id, type, title, optional audience_role, and TWO counts that answer different questions: `instance_count` (inbound `instance_of` edges from PRODUCT graphs) and `registry_edge_count` (the registry's own internal edges on either endpoint, written by `create_registry_edge`). A canonical with `instance_count: 0` is NOT necessarily unreferenced, so check `registry_edge_count` before treating one as safe to retire or re-point. With `include_instances` / `include_edges`, attaches the instances / registry-internal edges themselves. Empty when no registry exists yet.