### CHANGES
- Enhance user message conversion to support multi-content.
- Add capability to process image URLs in messages.
- Build multi-part messages with both text and images.
## CHANGES
- Extract shared message conversion to convertMessageCommon
- Reuse logic between chat and response APIs
- Maintain existing text-only behavior for chat
- Support multi-content messages in response API
- Reduce code duplication across converters
- Preserve backward compatibility for both APIs
## CHANGES
* Add chat completions API fallback for non-Responses API providers
* Implement `sendChatCompletions` and `sendStreamChatCompletions` methods
* Introduce `buildChatCompletionParams` to construct API request parameters
* Add `ImplementsResponses` flag to track provider API capabilities
* Update provider configurations with Responses API support status
* Enhance `Send` and `SendStream` methods to use appropriate API endpoints
- Replace chat completions with responses API
- Update message conversion to new format
- Refactor streaming to handle event types
- Remove frequency and presence penalty params
- Replace seed parameter with max tokens
- Update test cases for new API
- Add response text extraction method
### 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 slices import for array operations
- Define new search preview model names
- Add mini search preview variants
- Include deep research model support
- Add June 2025 dated model versions
- Replace hardcoded check with slices.Contains
- Support both prefix and exact model matching
## CHANGES
- Add model-specific raw mode detection logic
- Check Ollama llama2/llama3 models for raw mode
- Check OpenAI o1/o3/o4 models for raw mode
- Use model from options or default chatter
- Auto-enable raw mode when vendor requires it
- Import strings package for prefix matching
## 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
