fix: show and dismiss teacher introductions as one group

tests/e2e/teacher-preview-layout.spec.ts

@@ -79,15 +79,15 @@ for (const width of [375, 768, 1280]) {
       return !!bubble && !!viewport && viewport.y >= bubble.y + bubble.height;
     }).toBe(true);
     await page.screenshot({ path: test.info().outputPath(`teacher-introductions-${width}.png`) });
-    await group.getByRole('button', { name: '收起智能体2的介绍' }).click();
-    await expect(group.locator('.teacher-welcome-card')).toHaveCount(2);
+    await group.getByRole('button', { name: '收起全部老师介绍（智能体2）' }).click();
+    await expect(group).toHaveCount(0);
     await expect(page.locator('#coding-consultation-dock')).toHaveCount(0);
+    await page.reload();
+    await expect(group.locator('.teacher-welcome-card')).toHaveCount(3);
     await group.getByRole('button', { name: '和智能体3聊聊' }).click({ position: { x: 8, y: 8 } });
     await expect(page.getByRole('button', { name: '与智能体3聊天' })).toHaveAttribute('aria-pressed', 'true');
     await expect(group).toHaveCount(0);
     await page.getByRole('button', { name: '关闭智能体栏' }).click();
-    await expect(group.locator('.teacher-welcome-card')).toHaveCount(1);
-    while (await group.count()) await group.getByRole('button', { name: /^收起.*的介绍$/ }).first().click();
     await expect(group).toHaveCount(0);
   });
 }
@@ -108,8 +108,6 @@ test('many teacher introductions remain scrollable and honor reduced motion', as
   await page.keyboard.press('Enter');
   await expect(page.getByRole('button', { name: '与智能体8聊天' })).toHaveAttribute('aria-pressed', 'true');
   await page.getByRole('button', { name: '关闭智能体栏' }).click();
-  await expect(group.locator('.teacher-welcome-card')).toHaveCount(7);
-  while (await group.count()) await group.getByRole('button', { name: /^收起.*的介绍$/ }).first().click();
   await expect(group).toHaveCount(0);
 });