chore: prepare Better Auth UI 2.0.0

[olliethedev]

Summary

• prepare @btst/better-auth-ui 2.0.0 without publishing it
• require @btst/stack ^3.0.0 publicly while testing against the public 3.0.0-rc.4 gate
• retain the Better Auth 1.6.16/Core 1.6.16/Utils 0.4.1/Fetch 1.2.2/Call 1.3.6 cohort
• update package metadata coverage, lockfile, and BTST v3 stable installation guidance

Validation

• pnpm install --frozen-lockfile
• pnpm lint
• pnpm typecheck
• pnpm test (65 passed)
• pnpm run build
• docs pnpm install --frozen-lockfile
• docs pnpm build (68 static pages)
• packed tarball metadata and contents inspection
• git diff --check
• independent Standards review: no findings
• independent Spec review: no findings

The packed artifact reports @btst/better-auth-ui 2.0.0, @btst/stack peer ^3.0.0, and the expected root/server/client/tanstack/instantdb/triplit/CSS exports.

Release safety

This PR does not create a tag, GitHub release, or npm publication.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-01T00:33:11.591946Z	c264ddf	PR opened

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