feat(ai): add ai support

[aorinevo]

This pull request introduces AI-powered migration support to Shepherd, allowing users to describe code changes in natural language and have them applied automatically using AI models like Claude or OpenAI. It adds a new shepherd ai command, supporting configuration via both CLI and shepherd.yml, and provides comprehensive documentation and testing for the new feature. The most important changes are:

AI-Powered Migration Feature:

• Introduced the shepherd ai command, enabling users to apply migrations using natural language prompts and AI providers (claude or openai). The command supports options for provider, model, max tokens, and repo selection, and integrates with the existing migration workflow. [1] [2]
• Added new dependencies for AI integration: @anthropic-ai/sdk, openai, and file globbing support via glob. [1] [2] [3]

Documentation:

• Added detailed documentation for AI-powered migrations, including configuration examples, CLI usage, environment variables, best practices, troubleshooting, and comparison with traditional migrations in README.md, docs/ai-migrations.md, and docs/tutorial.md. [1] [2] [3]

Testing and Validation:

• Implemented comprehensive tests for the new ai command, covering provider validation, option merging, execution flow, and error handling.

These changes collectively enable a new, user-friendly way to perform complex, multi-repo code migrations using state-of-the-art AI models, with robust configuration and testing.

[aorinevo]

1. Fix CI
2. Test on local llama model on at 1 and multiple repos (at least 2)
3. Add documentation to run llama model locally