fix(openai): align image streaming relay governance

Route OpenAI image streaming through shared stream handling, split image/realtime/usage helpers for maintainability, and include the related image request and rate limit updates.

dto/openai_image.go

@@ -26,7 +26,7 @@ type ImageRequest struct {
 	OutputFormat      json.RawMessage `json:"output_format,omitempty"`
 	OutputCompression json.RawMessage `json:"output_compression,omitempty"`
 	PartialImages     json.RawMessage `json:"partial_images,omitempty"`
-	Stream            bool            `json:"stream,omitempty"`
+	Stream            *bool           `json:"stream,omitempty"`
 	Images            json.RawMessage `json:"images,omitempty"`
 	Mask              json.RawMessage `json:"mask,omitempty"`
 	InputFidelity     json.RawMessage `json:"input_fidelity,omitempty"`
@@ -163,7 +163,7 @@ func (i *ImageRequest) GetTokenCountMeta() *types.TokenCountMeta {
 }
 
 func (i *ImageRequest) IsStream(c *gin.Context) bool {
-	return i.Stream
+	return i.Stream != nil && *i.Stream
 }
 
 func (i *ImageRequest) SetModelName(modelName string) {

dto/openai_image_test.go

@@ -1,16 +0,0 @@
-package dto
-
-import (
-	"testing"
-
-	"github.com/stretchr/testify/require"
-)
-
-// TestImageRequestStreamJSON verifies that image requests preserve stream=true.
-func TestImageRequestStreamJSON(t *testing.T) {
-	var req ImageRequest
-	require.NoError(t, req.UnmarshalJSON([]byte(`{"model":"gpt-image-1","prompt":"draw a cat","stream":true}`)))
-
-	require.True(t, req.Stream)
-	require.True(t, req.IsStream(nil))
-}