feat(api): add OpenAI compatibility for image models

- Introduced OpenAI-compatible image model support in the API, enabling integration through image generation and editing endpoints.
- Added registry type for OpenAIImageModelType to classify and validate compatibility.
- Implemented request handling for OpenAI-compatible image models, including JSON and multipart formats.
- Enhanced executor methods to support OpenAI-compatible image streaming and non-streaming requests.
- Included tests to validate model registration, streaming behavior, and multipart payload formatting.

sdk/api/handlers/openai/codex_client_models.go

@@ -104,6 +104,9 @@ func applyCodexClientModelMetadata(entry map[string]any, id string, model map[st
 		if info.ContextLength > 0 {
 			contextWindow = info.ContextLength
 		}
+		if info.Type == registry.OpenAIImageModelType {
+			entry["visibility"] = "hide"
+		}
 		applyCodexClientThinkingMetadata(entry, info.Thinking)
 	}