Add dependencies for multi-LLM comparison tool

- Add gradio for UI framework
- Add OpenAI, Anthropic, Google, Cohere, Mistral API clients
- Add pandas for data handling and CSV export
- Add aiohttp for async HTTP requests

requirements.txt

@@ -0,0 +1,9 @@
+gradio>=4.0.0
+openai>=1.0.0
+anthropic>=0.18.0
+google-generativeai>=0.3.0
+cohere>=5.0.0
+mistralai>=0.1.0
+pandas>=2.0.0
+aiohttp>=3.9.0
+