/api/inkle/bookkeeping/group/{group_id}/entity/{entity_id}/interactive_report/variance_explanation/list/

Bulk-returns every explanation already stored for this entity/period (any depth — top-level,
sub-category, synthetic row, and the whole-report overview) as a flat list, in one cheap DB query
(no LLM calls). Used to repopulate previously-generated explanations on report reload.