### CHANGES
- Introduce local `chat` package for message abstraction
- Replace sashabaranov/go-openai with official openai-go SDK
- Update OpenAI, Azure, and Exolab plugins for new client
- Refactor all AI providers to use internal chat types
- Decouple codebase from third-party AI provider structs
- Replace deprecated `ioutil` functions with `os` equivalents
## CHANGES
- Add NeedsRawMode to Vendor interface
- Implement NeedsRawMode in all AI clients
- Return false for all implementations
- Support model-specific raw mode detection
- Enable future raw mode requirements
