List image-generation models available through OpenRouter

Image models live in their own upstream catalog and carry no published price — an image is billed at the exact cost OpenRouter reports on the generation response — so entries have no price_per_generation. When the upstream catalog published them, entries also carry architecture (input/output modalities) and supported_parameters (a typed descriptor map, e.g. resolution/seed) verbatim, for validating a request against this model's actual capabilities before submitting it.