feat: retrieval grounding, trial quality, and drug-name typo suggestions

feat: RRF merge + cross-encoder reranking for retrieval pipeline

fix(query): rank trials by status+relevance, raise cap from 5 to 10

feat: Stage 4 — entity extraction + knowledge graph + KG-expanded RAG

feat: Stage 3 — RAG pipeline + working end-to-end query

feat: initial project scaffold and Stage 2 ingestion pipeline