test(e2e): add GA4 tracking, mobile, user journey tests and update visual baselines

- Add GA4 event tracking E2E tests (4 cases: page view, form submit, button click, product page)
- Add mobile-specific E2E tests (16 cases: navigation, form, product browsing)
- Add user journey tests (UJ-01: homepage to contact, UJ-02: product discovery)
- Fix E2E test selectors and assertions for consistency
- Update visual regression baselines across all browsers (chromium/firefox/webkit)
- Update Playwright config for new test files

e2e/cms-workflow.spec.ts

@@ -258,7 +258,7 @@ async function verifyNewsVisibleOnFrontend(
   await expect(page.locator('body')).toContainText(`E2E 测试正文内容 ${suffix}`);
 }
 
-test.describe('CMS 内容发布工作流', () => {
+test.describe('CMS 内容发布工作流', { tag: '@critical' }, () => {
   // 同一 worker 内串行执行，避免共享 DB/角色权限在并行时相互影响
   test.describe.configure({ mode: 'serial' });