Replaces EmailJS-based welcome-back (disabled in PR #6 because the
EmailJS account is Melissa-only with obsolete '(c) 2025' footer) with
a Worker action that delegates to Resend, ensuring same '\xc2\xa9 2026'
footer as all other transactional emails.
Worker side:
- New action 'sendWelcomeBack' validates Turnstile + searches HubSpot
contact by email (404 if not found, prevents spam to non-existing).
- New function sendWelcomeBackViaResend: same navy/gold visual
identity as other Resend emails. Subject includes existing ref
(= 'Vous \xc3\xaates d\xc3\xa9j\xc3\xa0 inscrit chez MVA Global Fret \xe2\x80\x94 R\xc3\xa9f\xc3\xa9rence MVA-XXX').
Idempotent: zero HubSpot writes.
Frontend (form-handler.js):
- sendWelcomeBackEmail rewritten to POST Worker action sendWelcomeBack
instead of emailjs.send. Reuses window.turnstileToken.
- Re-enabled call inside showAlreadyRegistered.
Smoke tests:
- 400 'email requis' without email
- 403 'Turnstile validation failed' without valid token
- Full flow testable via browser only (= real Turnstile challenge).
Refs: post-cutover polish, fixes Issue 1 footer 2025 from E2E retest.
