Add comprehensive agentic workflow documentation

- Deep dive into tool-based architecture
- Explains LLM orchestration patterns
- Code walkthroughs with examples
- Comparison: traditional vs agentic
- Guide for extending the system
- Complete tool template

This 30+ page technical document explains:
- What agentic workflows are
- How tools work internally
- Execution flow end-to-end
- Context management
- Configuration system
- Advanced patterns (chaining, parallel, retry)

Author: claude