Fix dead homepage and announcement links

[shilman]

Problem

Ahrefs Site Audit (2026-07-12) found the homepage and SB9 announcement linking to removed showcase/video routes.

Broken links

Source URL	Target URL	Proposed fix
https://storybook.js.org/	https://storybook.js.org/showcase/shopify-polaris-react	Replace each link with its current destination. If the content was intentionally retired, remove the card/link rather than routing users to a 404.
https://storybook.js.org/	https://storybook.js.org/video	Replace each link with its current destination. If the content was intentionally retired, remove the card/link rather than routing users to a 404.
https://storybook.js.org/announce/sb9	https://storybook.js.org/showcase/glossary	Replace each link with its current destination. If the content was intentionally retired, remove the card/link rather than routing users to a 404.
https://storybook.js.org/announce/sb9	https://storybook.js.org/showcase/projects	Replace each link with its current destination. If the content was intentionally retired, remove the card/link rather than routing users to a 404.

Acceptance criteria

• Every source URL above resolves its linked destination without a 4XX response.
• Add/update a focused link-check regression test where the content pipeline supports it.
• Re-run the affected Site Audit report after deployment.