#3079
Change ModelPriceHelperPerCall to return (PriceData, error) and stop silently falling back to a default price. If a model price is not configured the helper now returns an error (unless the user has AcceptUnsetRatioModel enabled and a ratio exists). Propagate this error to callers: Midjourney handlers now return a MidjourneyResponse with Code 4 and the error message, and task submission returns a wrapped task error with HTTP 400. Also extract remix video_id in ResolveOriginTask for remix actions. This enforces explicit model price/ratio configuration and surfaces configuration issues to clients.
