feat: Add chat handler with RAG pipeline

- chat_handler.py: Standalone NATS handler with RAG
- chat_handler_v2.py: Handler-base implementation
- Dockerfiles for both versions

Pipeline: Embeddings → Milvus → Rerank → LLM → (optional TTS)

Dockerfile.v2

@@ -0,0 +1,11 @@
+# Chat Handler v2 - Using handler-base
+ARG BASE_TAG=local
+FROM ghcr.io/billy-davies-2/handler-base:${BASE_TAG}
+
+WORKDIR /app
+
+# Copy only the handler code (dependencies are in base image)
+COPY chat_handler_v2.py ./chat_handler.py
+
+# Run the handler
+CMD ["python", "chat_handler.py"]