feat: add multi-agent workflow tutorial with orchestration patterns

- Add Multi_Agent_Workflow.ipynb demonstrating agent collaboration
- Implement Agent and Tool base classes with OpenAI-compatible API support
- Create specialized agents: Researcher, Critic, and Writer with tool schemas
- Build MultiAgentOrchestrator for coordinating multi-step workflows
- Include advanced patterns: parallel execution, debate, and chain patterns
- Update agents/README.md with tutorial table and documentation

Author: Gaurav Singh