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/go.mod

@@ -10,7 +10,6 @@ require (
 	github.com/hibiken/asynq v0.26.0
 	github.com/jackc/pgx/v5 v5.8.0
 	github.com/minio/minio-go/v7 v7.2.1
-	github.com/oov/psd v0.0.0-20260122084234-c463b6a89e2f
 	github.com/redis/go-redis/v9 v9.19.0
 	github.com/sky-valley/pi v0.2.8
 	github.com/yalue/onnxruntime_go v1.22.0
@@ -29,7 +28,6 @@ require (
 	github.com/go-logr/logr v1.4.3 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
 	github.com/golang-jwt/jwt/v4 v4.5.2 // indirect
-	github.com/gopherjs/gopherjs v1.21.0 // indirect
 	github.com/grafana/pyroscope-go v1.3.0 // indirect
 	github.com/grafana/pyroscope-go/godeltaprof v0.1.10 // indirect
 	github.com/grpc-ecosystem/grpc-gateway/v2 v2.27.7 // indirect