Initial commit: img-infinite-canvas AI design workbench MVP

Moteva-style AI design workbench replica. Home prompt creates a project;
the project page provides an infinite canvas with node drag, zoom/pan,
a design chat panel, history replay, image asset upload, and project
save/regenerate.

- Backend: go-zero, DDD layering, sqlc/pgx, optional PostgreSQL; memory
  or Redis cache; asynq job queue; MinIO/S3/R2/OSS object storage;
  sky-valley/pi agent runtime adapter.
- Frontend: Next.js App Router + Vite artifact build, TypeScript, i18n,
  shadcn/ui components, auth (OTP/Turnstile/Google/WeChat).
- Deploy: Docker Compose and k3s manifests.

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

server/internal/domain/design/background_removal.go

@@ -0,0 +1,22 @@
+package design
+
+import "context"
+
+type BackgroundRemovalRequest struct {
+	Image       []byte
+	ContentType string
+	Width       int
+	Height      int
+	InputSize   int
+}
+
+type BackgroundRemoval struct {
+	Image       []byte
+	ContentType string
+	Width       int
+	Height      int
+}
+
+type BackgroundRemover interface {
+	RemoveBackground(ctx context.Context, req BackgroundRemovalRequest) (BackgroundRemoval, error)
+}