docs: enhance README with comprehensive documentation and improved structure

[open-swe-dev]

Summary

This PR significantly enhances the README.md file by transforming it from a basic 31-line document into a comprehensive 208-line professional documentation that provides complete guidance for users.

Changes Made

Structure & Organization

• Added project badges for LangGraph and Python version
• Created detailed table of contents with navigation links
• Organized content into logical sections with emoji icons for visual appeal

New Sections Added

• Features: Comprehensive list of agent capabilities
• Installation: Detailed setup instructions with prerequisites and step-by-step guide
• Configuration: Environment variables and model setup details
• Usage: Basic usage steps with example interaction dialogue
• Project Structure: File tree with descriptions of key components
• Troubleshooting: Common issues and solutions
• Contributing: Guidelines for project contributions
• Future Roadmap: Development directions

Content Improvements

• Enhanced project description with clearer explanation of the LangGraph Engineer's purpose
• Expanded "How It Works" section with detailed workflow explanations
• Improved deployment section with both LangGraph Cloud and local development options
• Added specific installation commands and configuration examples

Impact

This enhancement addresses all previously identified gaps in the documentation:

• ✅ Proper installation/setup instructions
• ✅ Detailed usage examples
• ✅ Project structure documentation
• ✅ Technical requirements and dependencies
• ✅ Configuration details
• ✅ Contributing guidelines
• ✅ Troubleshooting guidance
• ✅ Professional formatting and organization

The README now serves as a complete guide for users to understand, install, configure, and effectively use the LangGraph Engineer project.