This PR improves the environment variable handling in the Docker deployment, making the application more robust and configurable. It includes:

• Enhanced .env.sample file with comprehensive documentation
• Improved call_llm.py to better handle environment variables and error cases
• Updated Dockerfile with proper environment variable defaults
• Enhanced docker-compose.yml with volume mapping for cache file and explicit environment variables
• Added Git installation to Dockerfile to resolve GitPython dependency issues

These changes make the application more reliable when deployed in Docker containers and provide better documentation for users setting up their environment.