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

@@ -3,14 +3,16 @@ package design
 import "context"
 
 type AgentRequest struct {
-	Project    Project
-	Prompt     string
-	Mode       string
-	ImageModel string
-	ImageSize  string
-	Messages   []AgentChatMessage
-	Memory     AgentMemory
-	TaskPlan   AgentTaskPlan
+	Project      Project
+	Prompt       string
+	Mode         string
+	ImageModel   string
+	ImageSize    string
+	ImageQuality string
+	ImageCount   int
+	Messages     []AgentChatMessage
+	Memory       AgentMemory
+	TaskPlan     AgentTaskPlan
 }
 
 type AgentContent struct {
@@ -41,6 +43,8 @@ type AgentChatRequest struct {
 	EnableWebSearch       bool
 	ImageModel            string
 	ImageSize             string
+	ImageQuality          string
+	ImageCount            int
 	Mode                  string
 }
 
@@ -60,13 +64,33 @@ type AgentThreadSummary struct {
 }
 
 type GeneratorTaskInputArgs struct {
-	AspectRatio string
-	Image       []string
-	ImageURL    string
-	Prompt      string
-	Resolution  string
-	SrcBox      *NormalizedBox
-	DstBox      *NormalizedBox
+	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 {

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