RND-5646: section groups navigation menu

[BrettJephson]

This change adds grouped sections.

Horizontal section list:

CleanShot.2025-02-03.at.15.16.36.mp4

Vertical list:

CleanShot.2025-01-31.at.10.50.53.mp4

[linear]

RND-5646 Explore site sub sections dropdowns

[changeset-bot]

🦋 Changeset detected

Latest commit: d6cbc9d

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
gitbook	Patch

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[github-actions]

GitBook Preview
Latest commit: https://28ac2649.gitbook-open.pages.dev
PR: https://pr2789.gitbook-open.pages.dev

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Build	Status	Details	Updated (UTC)
default (Inspect)	👍 Changes approved	64 changed	Feb 4, 2025, 4:37 PM

[github-actions]

Summary of the deployments:

Version 1 (production)

Version	URL	Status
Latest commit	https://7447e455.gitbook-open.pages.dev	✅
PR	https://pr2789.gitbook-open.pages.dev	✅

Version 2 (experimental)

Version	URL	Status
Vercel	https://gitbook-v2-5z5wxhyzo-gitbook.vercel.app	✅
Cloudflare		✅

Test content

Site	v1	v2
GitBook	https://7447e455.gitbook-open.pages.dev/docs.gitbook.com	https://gitbook-v2-5z5wxhyzo-gitbook.vercel.app/static/url/docs.gitbook.com
E2E	https://7447e455.gitbook-open.pages.dev/gitbook.gitbook.io/test-gitbook-open	https://gitbook-v2-5z5wxhyzo-gitbook.vercel.app/static/url/gitbook.gitbook.io/test-gitbook-open

[emmerich]

We'll need to test the preview deployment on the docs we know using sections to ensure we haven't caused regressions

[BrettJephson]

Checking a few sections sites in preview:

https://pr2789.gitbook-open.pages.dev/docs.gitbook.com
https://pr2789.gitbook-open.pages.dev/support.braver.net
https://pr2789.gitbook-open.pages.dev/docs.onum.com
https://pr2789.gitbook-open.pages.dev/docs.seal.run/the-seal-platform

And Illumina who have lots of sections:
https://pr2789.gitbook-open.pages.dev/help.connected.illumina.com/dragen

[emmerich]

Would be good to see a visual test or two for the new UI

[BrettJephson]

Will add visual regression tests for sections and section groups in a separate PR.