Replace raw single-row fetch with aggregation over all pipeline_runs rows sharing the latest started_at. Returns structured object with regions[], sources_ok[], sources_error[], tracks_added instead of a raw DB row with region_id/source_id strings. Returns null when no runs exist (empty DB). Update test_i40_health_endpoint: add db_with_pipeline_runs fixture (two rows, same started_at, two regions) and assert the full aggregated shape including concrete values. Refs: ET-008 Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>