docs: add comprehensive guide to WARP for agentic development

New guide covers:
- 8 major use cases for agents (geo-location testing, rate limiting protection, agent communication, etc.)
- 3 implementation patterns with full code examples
- Performance considerations and best practices
- Advanced use cases (A/B testing, compliance, load testing, security testing)
- Integration with LangChain and multi-agent frameworks
- Common questions and answers

Demonstrates how warp-cli enables:
✅ Geographic location testing for agents
✅ API rate limiting protection
✅ Secure agent-to-agent communication
✅ Multi-region agent deployment
✅ CI/CD integration for agent testing
✅ Network bypass and filtering
✅ Split tunneling for selective routing
✅ Distributed agent networks

This opens up entirely new possibilities for agent development and testing.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

Author: ashu17706