Add SideSheet component, refactor TOC and AIChat to use it

[zenoachtig]

Also fixes RND-7803

[linear]

RND-7803 Better support for docs assistant on smaller screens

RND-7450 Mobile TOC + Chat layout

[changeset-bot]

🦋 Changeset detected

Latest commit: e329b41

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]

Summary of the deployments:

Version	URL	Status
Vercel	https://gitbook-v2-m7yc7fefb-gitbook.vercel.app	✅
Cloudflare	https://c6631c5d-gitbook-open-v2-preview.gitbook.workers.dev	✅

Test content

Site	2v	2c
GitBook	https://gitbook-v2-m7yc7fefb-gitbook.vercel.app/url/gitbook.com/docs	https://c6631c5d-gitbook-open-v2-preview.gitbook.workers.dev/url/gitbook.com/docs
E2E	https://gitbook-v2-m7yc7fefb-gitbook.vercel.app/url/gitbook.gitbook.io/test-gitbook-open	https://c6631c5d-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 detected (Review)	78 changed	Dec 5, 2025, 1:22 PM
v2-cloudflare (Inspect)	⚠️ Changes detected (Review)	390 changed	Dec 5, 2025, 1:25 PM
v2-vercel (Inspect)	⚠️ Changes detected (Review)	398 changed	Dec 5, 2025, 1:27 PM