Extends the checkout pattern (inline red error text, refocus on
submit if invalid) to all four newsletter-signup entry points. Two of
them (WeeklyImpulsesHero's inline hero form on /newsletter, and
/challenge's EmailCapture) turned out to be completely non-functional
before this too — same static-markup-with-no-onSubmit issue as
Newsletter.tsx/NewsletterModal.tsx had, just missed in the previous
pass since they're separate components sharing only the visual
pattern, not the code.
Consolidated the shared email+consent+submit state (previously
duplicated per-component) into useNewsletterSignup.ts, and pulled the
plain email-format regex (previously duplicated in CheckoutContent.tsx
and the subscribe route) into lib/email.ts as a single source of
truth. /challenge's EmailCapture is now its own client component
(app/challenge/components/EmailCapture.tsx) since its parent page is
an async Server Component and can't hold form state itself.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Marco