Support new object-fit property on individual card cover image

[viktorrenkema]

This PR implements the GBO-side of allowing the object-fit property on cards. Table record fields for cover image now not only accept api.ContentRefFile | api.ContentRefURL, but also an object that contains record-level configurations like object-fit where then the content ref will be nested:

export type TableDefinitionImageRecord =
    | api.ContentRefFile
    | api.ContentRefURL
    | {
          ref: api.ContentRefFile | api.ContentRefURL;
          objectFit?: api.CardsImageObjectFit;
      };

If an object-fit is used that results in the background of the card being visible, we apply a subtle bg tint-color of the configured customization styles.

see https://github.com/GitbookIO/gitbook-x/pull/19221

Preview

CleanShot.2025-08-25.at.09.40.03.mp4

[linear]

RND-7202 Card covers : aspect ratio is wrong

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Latest commit: 705ff63

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[github-actions]

Summary of the deployments:

Version	URL	Status
Vercel	https://gitbook-v2-9c9nwmk7g-gitbook.vercel.app	✅
Cloudflare	https://7ea74329-gitbook-open-v2-preview.gitbook.workers.dev	✅

Test content

Site	2v	2c
GitBook	https://gitbook-v2-9c9nwmk7g-gitbook.vercel.app/url/gitbook.com/docs	https://7ea74329-gitbook-open-v2-preview.gitbook.workers.dev/url/gitbook.com/docs
E2E	https://gitbook-v2-9c9nwmk7g-gitbook.vercel.app/url/gitbook.gitbook.io/test-gitbook-open	https://7ea74329-gitbook-open-v2-preview.gitbook.workers.dev/url/gitbook.gitbook.io/test-gitbook-open

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Build	Status	Details	Updated (UTC)
customers-v2 (Inspect)	👍 Changes approved	17 changed	Sep 3, 2025, 6:41 AM
v2-cloudflare (Inspect)	👍 Changes approved	15 changed	Sep 3, 2025, 6:44 AM
v2-vercel (Inspect)	👍 Changes approved	19 changed	Sep 3, 2025, 6:43 AM

[nolannbiron]

lgtm, just need to update the types once the API changes are released