修复确认生成后的任务列表对账

问题：客户端确认 Quote 后只刷新一次任务，遇到短暂投影延迟时任务列表为空且流程静默成功。

修复：按 quoteId 有界重试任务列表，合并 REST 与实时推送快照，缺任务时显示明确错误；补充 Store 与页面回归测试。

tests/unit/image-canvas-page.test.tsx

@@ -405,6 +405,7 @@ describe('ImageCanvas Workspace-first design experience', () => {
       .mockResolvedValueOnce([{
         ...taskFixture,
         taskId: 'task-two',
+        quoteId: 'quote-one',
         status: 'queued',
         resultAssets: [],
       }]);
@@ -421,6 +422,7 @@ describe('ImageCanvas Workspace-first design experience', () => {
         expect.stringMatching(/^turn-/),
       ));
     await waitFor(() => expect(fetchImageWorkspaceTasksMock).toHaveBeenCalledTimes(2));
+    expect(await screen.findByTestId('design-task-task-two')).toBeInTheDocument();
   });
 
   it('renders a new task pushed by the design event stream without repeated polling', async () => {