Element: #843 Sign-in form (inputs/turnstile)
What it shows: A sign-in form with a Turnstile captcha: no token without the check, reset() after a submit.
When to use: Public forms (sign-in, sign-up, waitlist, reset) that need a captcha token to verify on the server.
Spec:
- `import { Turnstile, type TurnstileHandle } from '@codeatlasdev/ui/forms'`
- `const SITE_KEY = '1x00000000000000000000AA'` (Cloudflare's always-pass test key)
- `