Handle non-defined objectFit on card cover images

[viktorrenkema]

We added support for setting objectFit on card covers. But if those were never defined yet, the current logic fell short in that we wouldnt handle a default value. This PR ensures that if no object-fit was set, we default to 'cover' which we always had before.

Before:

After:

~closes https://linear.app/gitbook-x/issue/RND-8043/inconsistent-card-image-rendering-on-published-site

[linear]

RND-8043 Inconsistent card image rendering on published site

[changeset-bot]

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Latest commit: ae25751

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[github-actions]

Summary of the deployments:

Version	URL	Status
Vercel	https://gitbook-v2-f2s3gyout-gitbook.vercel.app	✅
Cloudflare	https://7827b986-gitbook-open-v2-preview.gitbook.workers.dev	✅

Test content

Site	2v	2c
GitBook	https://gitbook-v2-f2s3gyout-gitbook.vercel.app/url/gitbook.com/docs	https://7827b986-gitbook-open-v2-preview.gitbook.workers.dev/url/gitbook.com/docs
E2E	https://gitbook-v2-f2s3gyout-gitbook.vercel.app/url/gitbook.gitbook.io/test-gitbook-open	https://7827b986-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 5, 2025, 8:30 AM
v2-cloudflare (Inspect)	👍 Changes approved	15 changed	Sep 5, 2025, 8:34 AM
v2-vercel (Inspect)	👍 Changes approved	20 changed	Sep 5, 2025, 8:42 AM