qrst: On-Device Hybrid Search

qrst is a hybrid search engine that runs entirely on-device. No API calls, no cloud, just a Rust binary and an embedding model. It combines BM25 keyword search (SQLite FTS5) with vector semantic search (ONNX embeddings + HNSW) and fuses results using configurable strategies including Reciprocal Rank Fusion and learned-to-rank models.