feat(canvas): build PSD export in the browser from canvas layers

Move PSD generation off the server. The image-generation API only
produces raster formats, so drop the PSD request path, the oov/psd
decoder, and the LayeredDocumentGenerator wiring. Layer separation now
returns clean background, foreground, and text_render_data artifacts
into a transparent frame.

Export that frame (or any image node) as PSD from the canvas context
menu: ag-psd assembles layers, rotation/flip, opacity, editable text,
and stroke effects from the current canvas state at download time.

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

server/internal/application/design_service.go

@@ -51,26 +51,25 @@ const nodeActionResultNodeIDOption = "_resultNodeId"
 const generationRecoveryToolHint = "generation_recovery"
 
 type DesignService struct {
-	repo                     design.Repository
-	agent                    design.AgentRunner
-	assets                   design.AssetStorage
-	assetCleanup             *assetCleanupQueue
-	jobs                     design.JobQueue
-	search                   design.Researcher
-	textExtractor            design.TextExtractor
-	objectRecognizer         design.ObjectRecognizer
-	imageVectorizer          design.ImageVectorizer
-	backgroundRemover        design.BackgroundRemover
-	layeredDocumentGenerator design.LayeredDocumentGenerator
-	mockupAnalyzer           design.MockupModelAnalyzer
-	textExtractionCache      textExtractionCacheStore
-	textExtractionCacheTTL   time.Duration
-	creativeAgent            design.CreativeAgent
-	cancelledAgentTasks      sync.Map
-	agentTaskCancels         sync.Map
-	generatorTaskMu          sync.RWMutex
-	generatorTasks           map[string]design.GeneratorTask
-	now                      func() time.Time
+	repo                   design.Repository
+	agent                  design.AgentRunner
+	assets                 design.AssetStorage
+	assetCleanup           *assetCleanupQueue
+	jobs                   design.JobQueue
+	search                 design.Researcher
+	textExtractor          design.TextExtractor
+	objectRecognizer       design.ObjectRecognizer
+	imageVectorizer        design.ImageVectorizer
+	backgroundRemover      design.BackgroundRemover
+	mockupAnalyzer         design.MockupModelAnalyzer
+	textExtractionCache    textExtractionCacheStore
+	textExtractionCacheTTL time.Duration
+	creativeAgent          design.CreativeAgent
+	cancelledAgentTasks    sync.Map
+	agentTaskCancels       sync.Map
+	generatorTaskMu        sync.RWMutex
+	generatorTasks         map[string]design.GeneratorTask
+	now                    func() time.Time
 }
 
 type agentTaskCancelHandle struct {
@@ -137,10 +136,6 @@ func (s *DesignService) SetBackgroundRemover(remover design.BackgroundRemover) {
 	s.backgroundRemover = remover
 }
 
-func (s *DesignService) SetLayeredDocumentGenerator(generator design.LayeredDocumentGenerator) {
-	s.layeredDocumentGenerator = generator
-}
-
 func (s *DesignService) SetObjectRecognizer(recognizer design.ObjectRecognizer) {
 	s.objectRecognizer = recognizer
 }