Add knowledge base RAG module for book Q&A

- Create knowledge.py handler with dynamic book selection
- Support list/select/query actions for multiple books
- Implement vector search with cosine similarity
- Add knowledge detection to AI parser config
- Cache embeddings per-book for performance
- Add numpy dependency for vector operations

requirements.txt

@@ -9,3 +9,4 @@ requests>=2.31.0
 pytest>=7.0.0
 pytest-asyncio>=0.21.0
 pywebpush>=1.14.0
+numpy>=1.26.0