fix(regression): resolve dogfood findings across marketing, auth, e2e and docs

- Fix list-to-detail navigation on product/service/solution/case pages
- Fix soft 404 on service detail by removing (marketing)/loading.tsx and using force-dynamic
- Fix contact form submission feedback and news placeholder image handling
- Unify SSR/client authentication state in auth.ts
- Add "新闻动态" to main navigation
- Fix Playwright storageState path and Firefox footer link flakiness
- Add E2E coverage for nav dropdown, cases filter and auth token parsing
- Update visual regression baselines (desktop/tablet/mobile, chromium/webkit/firefox)
- Update README, lessons-learned and add REGRESSION_REPORT_2026-07-27.md
- Ignore .lighthouseci/ and heading-hierarchy-report.json

.gitignore

@@ -250,6 +250,7 @@ test-email.js
 test-screenshot.png
 hero-check.png
 playwright-test-not-portal.js
+heading-hierarchy-report.json
 
 # Test reports
 reports/e2e/
@@ -258,6 +259,7 @@ reports/coverage/
 
 # Performance audit results
 lighthouse-reports/
+.lighthouseci/
 performance-baseline.json
 
 # Test data exports