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.

internal/runtime/executor/codex_executor.go

@@ -147,6 +147,9 @@ func (e *CodexExecutor) Execute(ctx context.Context, auth *cliproxyauth.Auth, re
 	if opts.Alt == "responses/compact" {
 		return e.executeCompact(ctx, auth, req, opts)
 	}
+	if isCodexOpenAIImageRequest(opts) {
+		return e.executeOpenAIImage(ctx, auth, req, opts)
+	}
 	baseModel := thinking.ParseSuffix(req.Model).ModelName
 
 	apiKey, baseURL := codexCreds(auth)
@@ -397,6 +400,9 @@ func (e *CodexExecutor) ExecuteStream(ctx context.Context, auth *cliproxyauth.Au
 	if opts.Alt == "responses/compact" {
 		return nil, statusErr{code: http.StatusBadRequest, msg: "streaming not supported for /responses/compact"}
 	}
+	if isCodexOpenAIImageRequest(opts) {
+		return e.executeOpenAIImageStream(ctx, auth, req, opts)
+	}
 	baseModel := thinking.ParseSuffix(req.Model).ModelName
 
 	apiKey, baseURL := codexCreds(auth)