fix: update requirements.txt with complete dependencies for HF Spaces

Add all cascade package dependencies needed for the UI to work:
- FastAPI and uvicorn for potential API integration
- Redis and Qdrant clients for caching layer
- OpenAI SDK for LLM providers
- Transformers and ML packages for routing classifier
- All UI dependencies (streamlit, plotly, pandas)

This ensures the Streamlit app can import cascade modules without
errors when deployed to Hugging Face Spaces.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

requirements.txt

@@ -1,6 +1,30 @@
-streamlit==1.31.0
+# Core dependencies
+fastapi==0.109.0
+uvicorn[standard]==0.27.0
 httpx==0.26.0
-plotly==5.18.0
-pandas==2.1.4
 pydantic==2.5.3
 pydantic-settings==2.1.0
+python-dotenv==1.0.0
+
+# LLM providers
+openai==1.10.0
+
+# Caching
+redis==5.0.1
+qdrant-client==1.7.3
+
+# ML and embeddings
+sentence-transformers==2.2.2
+transformers==4.37.2
+torch==2.1.2
+onnx==1.15.0
+onnxruntime==1.16.3
+scikit-learn==1.4.0
+
+# UI
+streamlit==1.31.0
+plotly==5.18.0
+pandas==2.1.4
+
+# Monitoring
+prometheus-client==0.19.0