Pull latest entities to the graph

Adds documents to a graph by copying their entities and relationships. This endpoint: 1. Copies document entities to the graphs_entities table 2. Copies document relationships to the graphs_relationships table 3. Associates the documents with the graph When a document is added: - Its entities and relationships are copied to graph-specific tables - Existing entities/relationships are updated by merging their properties - The document ID is recorded in the graph's document_ids array Documents added to a graph will contribute their knowledge to: - Graph analysis and querying - Community detection - Knowledge graph enrichment The user must have access to both the graph and the documents being added.