feat(design): thread image quality, count and layered output through domain

Add ImageQuality/ImageCount to AgentRequest, AgentChatRequest and Job,
add OutputFormat to GeneratorTaskInputArgs, and introduce the
LayeredDocument types and LayeredDocumentGenerator port for PSD output.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/internal/domain/design/agent.go

@@ -8,6 +8,8 @@ type AgentRequest struct {
 	Mode         string
 	ImageModel   string
 	ImageSize    string
+	ImageQuality string
+	ImageCount   int
 	Messages     []AgentChatMessage
 	Memory       AgentMemory
 	TaskPlan     AgentTaskPlan
@@ -41,6 +43,8 @@ type AgentChatRequest struct {
 	EnableWebSearch       bool
 	ImageModel            string
 	ImageSize             string
+	ImageQuality          string
+	ImageCount            int
 	Mode                  string
 }
 
@@ -63,12 +67,32 @@ type GeneratorTaskInputArgs struct {
 	AspectRatio  string
 	Image        []string
 	ImageURL     string
+	OutputFormat string
 	Prompt       string
 	Resolution   string
 	SrcBox       *NormalizedBox
 	DstBox       *NormalizedBox
 }
 
+type LayeredDocumentRequest struct {
+	ImageURL       string
+	Prompt         string
+	Model          string
+	Size           string
+	OutputFormat   string
+	IdempotencyKey string
+}
+
+type LayeredDocument struct {
+	Content     string
+	ContentType string
+	Data        []byte
+}
+
+type LayeredDocumentGenerator interface {
+	GenerateLayeredDocument(ctx context.Context, req LayeredDocumentRequest) (LayeredDocument, error)
+}
+
 type GeneratorTaskSubmitRequest struct {
 	CID           string
 	ProjectID     string

server/internal/domain/design/jobs.go

@@ -24,6 +24,8 @@ type Job struct {
 	Mode            string
 	ImageModel      string
 	ImageSize       string
+	ImageQuality    string
+	ImageCount      int
 	TaskPlan        AgentTaskPlan
 	EnableWebSearch bool
 	Isolated        bool