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)

.gitignore

@@ -0,0 +1,26 @@
+# Python
+__pycache__/
+*.py[cod]
+*$py.class
+*.so
+.Python
+build/
+dist/
+*.egg-info/
+*.egg
+
+# Virtual environments
+venv/
+.venv/
+ENV/
+
+# IDE
+.idea/
+.vscode/
+*.swp
+*~
+
+# Local
+.env
+.env.local
+*.log