Backend MVP: FastAPI + Claude integration

Core components:
- FastAPI server with health endpoints
- AI client (Anthropic Claude integration)
- Context manager (loads company knowledge)
- Chat API (non-streaming and streaming)
- Requirements and environment setup

Ready to run: python backend/main.py

backend/requirements.txt

@@ -0,0 +1,13 @@
+fastapi==0.109.0
+uvicorn[standard]==0.27.0
+anthropic==0.18.1
+python-dotenv==1.0.0
+pydantic==2.5.3
+pydantic-settings==2.1.0
+python-multipart==0.0.6
+aiofiles==23.2.1
+GitPython==3.1.41
+PyYAML==6.0.1
+markdown==3.5.2
+weasyprint==60.2
+pandas==2.2.0