fix(openai): support streaming image relay and image edit for images API (#4608)

* fix(openai): support streaming image relay

* fix(openai): keep image edit multipart body reusable

* test(openai): cover image stream usage details

* test(openai): cover image edit fallback stream field

* fix(openai): wrap image json fallback as stream

* fix(relay): support OpenAI image streaming

* fix(openai): record image stream upstream error events

* fix(openai): harden image stream relay

* fix(openai): return image JSON errors

* fix(relay): reset stream status per scanner run

* fix(relay): drop upstream credit passthrough

* fix(openai): keep image errors minimal

* fix(openai): keep image error status from response

---------

Co-authored-by: CaIon <i@caion.me>

dto/openai_image_test.go

@@ -0,0 +1,16 @@
+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))
+}