Phase 6.5: Pipeline telemetry, search UX fixes, latency profiling

Phase 6.5: Documentation finalization

Phase 6.3: Bug B fix + documentation finalization

Phase 6: LightGBM reranker integration (37-feature schema, 141-tree model)

Phase 4 complete + Phase 4.5 instrumentation foundation

docs: Update tracker - Phase 3.5 fully complete, all integration done

docs: Add Phase 3.5 Turso ArXiv Metadata DB, update infra status

Phase 3 complete: Hybrid Semantic Search pipeline