mushuiyu_xydt's commit 0e1ef93e84 (#61155) routes MiniMax image
generation requests to the dedicated image endpoint
(api.minimax.io/v1/image_generation), ignoring models.providers.minimax.baseUrl
(which targets the chat/Anthropic-compatible API), and adds
MINIMAX_API_HOST support for the CN api.minimaxi.com endpoint. The
CHANGELOG entry covered it but docs/providers/minimax.md image-generation
section did not. Add a paragraph naming both endpoints and the
MINIMAX_API_HOST override.