Add AI chat reference button on text selection

[nolannbiron]

Selecting text in the page content shows a floating "Ask" button that stages the selection as a reference and opens the AI chat. Desktop only (Assistant mode).

[changeset-bot]

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Latest commit: 04ab8e4

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[github-actions]

Summary of the deployments:

Version	URL	Status
Vercel	https://gitbook-v2-8p2e9h1bf-gitbook.vercel.app	✅
Cloudflare	https://e54b790c-gitbook-open-v2-preview.gitbook.workers.dev	✅

Test content

Site	2v	2c
GitBook	https://gitbook-v2-8p2e9h1bf-gitbook.vercel.app/url/gitbook.com/docs	https://e54b790c-gitbook-open-v2-preview.gitbook.workers.dev/url/gitbook.com/docs
E2E	https://gitbook-v2-8p2e9h1bf-gitbook.vercel.app/url/gitbook.gitbook.io/test-gitbook-open	https://e54b790c-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-cloudflare (Inspect)	✅ No changes detected	-	Jun 18, 2026, 11:24 PM
customers-v2-vercel (Inspect)	👍 Changes approved	1 changed	Jun 18, 2026, 11:23 PM
v2-cloudflare (Inspect)	✅ No changes detected	-	Jun 18, 2026, 11:29 PM
v2-vercel (Inspect)	✅ No changes detected	-	Jun 18, 2026, 11:29 PM