Scene hierarchy: parentId with local positions, tree panel, reparenting and Parent node

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

tests/core/serialize.test.ts

@@ -52,7 +52,7 @@ describe('serialize', () => {
       name: '',
       position: { x: 5, y: 0, z: 0 },
       overrides: { color: 0x00ff00, width: 1 },
-      ownerId: '',
+      parentId: '',
     });
     expect(project.assets[1]!.name).toBe('sprite');
     expect(project.assets[1]!.props).toEqual({ width: 10, height: 100, color: 0xe0553f });