[tomchen]

Summary

Complete missing sharing and article metadata, add sitemap dates from reviewed content, and fix broken structured breadcrumbs. Correct keyboard focus, search contrast, and accessible names across the English and Chinese interfaces.

Expand automated accessibility coverage to all reported WCAG 2.2 AA violations, interactive review cards, search failure states, and desktop/mobile keyboard flows. Require Lighthouse accessibility, best practices, and SEO scores of 100 while retaining the performance floor of 95 and existing script budgets. Preserve CI reports on successful runs as well as failures.

Developer guidance and explanatory comments now use English. The local validation record is tracked in docs/dev/seo-a11y-validation-2026-09-22.md.

Validation

• Local lint, type checks, production build, and internal-link checks passed.
• 2,427 unit tests and 364 Chromium browser tests passed.
• 155,274 internal links and structured-data destinations resolve; metadata and image checks cover 5,909 pages and 2,349 sharing images.
• Full Lighthouse validation is pending GitHub CI. Local measurements were stopped at the user's request to release browser resources; the Python hub's single performance score of 88 remains unconfirmed.

Checklist

• English and Chinese interfaces are covered; bilingual teaching content was not changed.
• Topic checks and example execution are not applicable: no topics or runnable examples changed.
• The relevant local project gates in CONTRIBUTING.md pass.
• The complete Lighthouse gate passes in GitHub CI.