修复画布编辑器测试会话隔离

在画布编辑器测试开始前清理 sessionStorage，避免项目快照跨用例污染

验证素材批量删除与关联图层清理测试在完整测试文件中稳定通过

src/components/image-editor/ImageCanvasEditorView.test-utils.ts

@@ -232,6 +232,7 @@ export function setupImageCanvasEditorViewTestLifecycle({
   saveEditorProjectLayoutMock,
 }: ImageCanvasEditorViewServiceMocks) {
   beforeEach(() => {
+    window.sessionStorage.clear();
     vi.spyOn(HTMLCanvasElement.prototype, 'getContext').mockReturnValue(null);
     loadOrCreateRecentEditorProjectMock.mockImplementation(() =>
       immediateAsync({