feat(image): pass reference images to GPT image model for edits

Server: forward canvas/reference images to the image model so extract,
continue, and edit requests stay faithful to the source product.
- Add ImageRequestOptions.Images and route requests with inputs to the
  /v1/images/edits endpoint, via multipart upload (default) or JSON
  image_url payload, selectable through Agent.Image.InputImageTransport.
- Extract reference URLs from prompt directives, inline @image tokens,
  and chat message image/mask contents; fold them into the idempotency
  key and prepend a reference-fidelity instruction to the prompt.

Frontend:
- Shrink CanvasToast to a compact top pill.
- Paste an internal transparent clipboard node instead of re-uploading
  when it matches the clipboard image.
- Keep agent-project polling alive on stream error while streaming.

server/internal/infrastructure/piagent/design_agent_test.go

@@ -214,6 +214,52 @@ func TestDesignAgentGeneratesImageThroughPiAgent(t *testing.T) {
 	}
 }
 
+func TestDesignAgentPassesInlineReferenceImagesToImageGenerator(t *testing.T) {
+	imageGenerator := &fakeImageGenerator{}
+	agent := NewDesignAgent(fakeRunner{}, imageGenerator, fakeCreativeAgent{})
+
+	_, err := agent.Plan(context.Background(), design.AgentRequest{
+		Prompt:     "把参考图里的灰裤子拆成单件商品图",
+		Mode:       "image",
+		ImageModel: "gpt-image-2",
+		Messages: []design.AgentChatMessage{
+			{
+				Role: "user",
+				Contents: []design.AgentContent{
+					{Type: "image", ImageURL: "https://example.com/pants-rack.png", ImageWidth: 1200, ImageHeight: 900},
+					{Type: "text", Text: "把参考图里的灰裤子拆成单件商品图", TextSource: "input"},
+				},
+			},
+		},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(imageGenerator.opts.Images) != 1 || imageGenerator.opts.Images[0] != "https://example.com/pants-rack.png" {
+		t.Fatalf("expected reference image to be passed to GPT Image 2, got %#v", imageGenerator.opts.Images)
+	}
+	if !strings.Contains(imageGenerator.prompt, "参考图") {
+		t.Fatalf("expected prompt to tell image model to use attached reference, got %s", imageGenerator.prompt)
+	}
+}
+
+func TestDesignAgentPassesPromptDirectiveReferenceImagesToImageGenerator(t *testing.T) {
+	imageGenerator := &fakeImageGenerator{}
+	agent := NewDesignAgent(fakeRunner{}, imageGenerator, fakeCreativeAgent{})
+
+	_, err := agent.Plan(context.Background(), design.AgentRequest{
+		Prompt:     "参考图 1（image）：https://example.com/pants-rack.png\n灰裤子拆成单件衣服，为了后面电商配图。",
+		Mode:       "image",
+		ImageModel: "gpt-image-2",
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(imageGenerator.opts.Images) != 1 || imageGenerator.opts.Images[0] != "https://example.com/pants-rack.png" {
+		t.Fatalf("expected directive reference image to be passed to GPT Image 2, got %#v", imageGenerator.opts.Images)
+	}
+}
+
 func TestDesignAgentUsesDefaultImageSizeWithoutExplicitRequest(t *testing.T) {
 	imageGenerator := &fakeImageGenerator{}
 	agent := NewDesignAgent(fakeRunner{}, imageGenerator, fakeCreativeAgent{})