feat(commands): add transparent artboard creation

commands/document.test.ts

@@ -0,0 +1,22 @@
+import { describe, expect, test } from "bun:test";
+import { createInitialAppState } from "@editor/initial-state";
+import { documentAddArtboardCommand } from "./document";
+
+describe("document commands", () => {
+  test("adds transparent artboard", () => {
+    const next = documentAddArtboardCommand.execute(
+      { state: createInitialAppState("Test") },
+      { id: "a1", name: "Artboard 1", bounds: { x: 0, y: 0, w: 320, h: 240 } },
+    );
+
+    expect(next.document.artboards).toEqual([
+      {
+        id: "a1",
+        name: "Artboard 1",
+        bounds: { x: 0, y: 0, w: 320, h: 240 },
+        backgroundColor: "transparent",
+        layers: [],
+      },
+    ]);
+  });
+});