Support custom page cover heights on docs site

[viktorrenkema]

Summary

• add shared helpers to normalize page cover height metadata
• render page covers using the configured height and hide them when set to zero
• ensure layouts and image styles respect the dynamic cover height

Testing

• bunx biome check packages/gitbook/src/components/PageBody/coverHeight.ts packages/gitbook/src/components/PageBody/PageCover.tsx packages/gitbook/src/components/PageBody/PageCoverImage.tsx packages/gitbook/src/components/PageBody/PageBody.tsx packages/gitbook/src/components/SitePage/SitePage.tsx

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https://chatgpt.com/codex/tasks/task_b_68e7f162517c83209b5a8ee9871f00cb

[changeset-bot]

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Latest commit: 88fe9e9

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[github-actions]

Summary of the deployments:

Version	URL	Status
Vercel		❌
Cloudflare		❌

Test content

Site	2v	2c
GitBook	/url/gitbook.com/docs	/url/gitbook.com/docs
E2E	/url/gitbook.gitbook.io/test-gitbook-open	/url/gitbook.gitbook.io/test-gitbook-open