gemini-3-pro-image-preview nondeterministically returns image/jpeg
instead of image/png. get_image_from_response() hardcoded
get_parts_by_type(response, "image/png"), silently dropping JPEG
responses and falling back to torch.zeros (all-black output).
Add _mime_matches() helper using fnmatch for glob-style MIME matching.
Change get_image_from_response() to request "image/*" so any image
format returned by the API is correctly captured.
185c61dc26