ofox-image-core: Ofox image API execution layer

Wraps the Ofox image generation API (https://api.ofox.ai/v1/images/generations) behind one script: validate, request, decode, save, report real token usage. Unlike ofox-video-core, this API is synchronous — one request either returns the finished image(s) in the response body or fails outright. There is no job id, no polling, and (because of that) no free "check what happened" recovery path if a request goes wrong mid-flight.

Safety contract (non-negotiable)