feat: switch retrieval to knowledge-graph GraphRAG

feat: add /vector_store_status endpoint for qdrant health and point count

feat: add GET /chunks endpoint with pagination and keyword filter

feat: add /chunk_context endpoint to expose neighbouring chunks

feat: grounded answering with confidence metadata and strict mode

feat: streaming LLM responses via SSE /query/stream endpoint

fix: embedding shape for query + add LLM error logging

initial deploy