Complete GraphRAG Implementation Guide with Neo4j and LangChain

Complete implementation: Step 1 Setup (install packages, configure connections), Step 2 Document Processing (load and split documents), Step 3 Knowledge Graph Construction (LLMGraphTransformer to extract entities), Step 4 Vector Indexing (create Neo4j vector index), Step 5 Community Detection (run Leiden via GDS), Step 6 Retrieval Pipeline (VectorCypherRetriever), Step 7 Query Interface (combine retrieval with LLM generation).