feat: add core domain model foundations

core/artboard.ts

@@ -0,0 +1,11 @@
+import type { Rect } from "./geometry";
+import type { ArtboardId } from "./id";
+import type { Layer } from "./layer";
+
+export type Artboard = {
+  id: ArtboardId;
+  name: string;
+  bounds: Rect;
+  backgroundColor: string;
+  layers: Layer[];
+};