Update button sizing

[zenoachtig]

• Button now uses T-shirt size names ((x)small/medium/large), and renders them with the same dimensions as the upcoming Input component, so they look good side-by-side.
• Reworks the dimensions of medium and large to be more distinct from each other and each size individually more useful.
• Remove hardcoded button overrides
• Makes medium the default button size, update buttons across the app

[changeset-bot]

🦋 Changeset detected

Latest commit: cfef647

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-b09gj313n-gitbook.vercel.app	✅
Cloudflare	https://5e24b21c-gitbook-open-v2-preview.gitbook.workers.dev	✅

Test content

Site	2v	2c
GitBook	https://gitbook-v2-b09gj313n-gitbook.vercel.app/url/gitbook.com/docs	https://5e24b21c-gitbook-open-v2-preview.gitbook.workers.dev/url/gitbook.com/docs
E2E	https://gitbook-v2-b09gj313n-gitbook.vercel.app/url/gitbook.gitbook.io/test-gitbook-open	https://5e24b21c-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)	80 changed	Dec 12, 2025, 3:01 PM
v2-cloudflare (Inspect)	⚠️ Changes detected (Review)	682 changed	Dec 12, 2025, 3:05 PM
v2-vercel (Inspect)	⚠️ Changes detected (Review)	686 changed	Dec 12, 2025, 3:05 PM