feat(piagent): support image quality and output_format in image client

Add quality and output_format to ImageRequestOptions, plumb them through
the JSON/multipart request bodies, generalize asset URL collection to
non-image formats, and add GenerateLayeredDocument for PSD output.

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

server/internal/infrastructure/piagent/design_agent.go

@@ -303,6 +303,9 @@ func (a *DesignAgent) buildImagePrompts(ctx context.Context, req design.AgentReq
 
 func plannedGenerationCount(req design.AgentRequest) int {
 	count := req.TaskPlan.ImageCount
+	if count <= 0 && req.ImageCount > 0 {
+		count = req.ImageCount
+	}
 	if count <= 0 && len(req.TaskPlan.ImageTasks) > 0 {
 		count = len(req.TaskPlan.ImageTasks)
 	}
@@ -516,6 +519,7 @@ func (a *DesignAgent) generateImageWithFallbackCount(ctx context.Context, req de
 	image, err := a.imageAgent.Generate(ctx, prompt, ImageRequestOptions{
 		Model:          req.ImageModel,
 		Size:           req.ImageSize,
+		Quality:        req.ImageQuality,
 		Count:          count,
 		Images:         referenceImages,
 		IdempotencyKey: imageGenerationIdempotencyKey(req, index, prompt, false),
@@ -532,6 +536,7 @@ func (a *DesignAgent) generateImageWithFallbackCount(ctx context.Context, req de
 	fallbackImage, fallbackErr := a.imageAgent.Generate(ctx, fallback, ImageRequestOptions{
 		Model:          req.ImageModel,
 		Size:           req.ImageSize,
+		Quality:        req.ImageQuality,
 		Count:          count,
 		Images:         referenceImages,
 		IdempotencyKey: imageGenerationIdempotencyKey(req, index, fallback, true),
@@ -553,6 +558,7 @@ func imageGenerationIdempotencyKey(req design.AgentRequest, index int, prompt st
 		strings.TrimSpace(req.Prompt),
 		strings.TrimSpace(req.ImageModel),
 		strings.TrimSpace(req.ImageSize),
+		strings.TrimSpace(req.ImageQuality),
 		strconv.Itoa(plannedGenerationCount(req)),
 		strconv.Itoa(index),
 		kind,