fix(rag-api): relax keyword overlap filter + cache DeBERTa intent results

feat: numbered citations [1][2][3], follow-up questions, focus modes

feat: Add query enhancements and flexible prompting (v2.1)

fix: make _build_context and execute_chat async for hybrid search

fix: use await instead of asyncio.run for hybrid search

fix: add missing logger import in rag_chat_use_case

feat(rag): implement hybrid search with live sources and production-grade intent classification