v0.19.0

The backend end-of-life release: understand-anything and cognee are fully removed — the typed ResearchGraph pipeline and the LLM retrieval planner have owned the default KG update and retrieval loop since 0.18.0, so the two bolted-on backends that duplicated it are gone (net −5,500 lines; every removed surface prints a one-line replacement stub and exits 2; legacy configs load with a single note). rag-anything stays as the optional multimodal-RAG extra. Full notes: docs/release-notes/v0.19.0.md (7 translations included).