fix: serialize concurrent thread access to in-memory SQLite connection to prevent race conditions and deadlocks

feat: implement Search Architecture V3 (Hybrid search with Qwen query transformation, batch embeddings, batch Qdrant searches, and optimized CPU reranking)

feat: normalize reference extraction and popup UI

Expand POPULAR_TERMS: 40 -> 293 via 84000.org dictionary

Deploy React+FastAPI webapp to HF Space