* feat(image-tool): support multiple images in a single tool call
- Change 'image' parameter to accept string | string[] (Type.Union)
- Add 'maxImages' parameter (default 5) to cap abuse/token explosion
- Update buildImageContext to create multiple image content parts
- Normalize single string input to array for unified processing
- Keep full backward compatibility: single string works as before
- Update tool descriptions for both vision and non-vision models
- MiniMax VLM falls back to first image (single-image API)
- Details output adapts: 'image' key for single, 'images' for multi
* bump default max images from 5 to 20
ff4f59ec90