refactor(worker): migrate Brevo+EmailJS → Resend + remove cron + fix github.io URLs
- Replace Brevo HTTP API calls with Resend (api.resend.com/emails) — aligns with m4s-auth Phase 2.1 SMTP provider
- Remove scheduled handler and processWelcomeQueue (EmailJS cron */5 * * * *)
→ eliminates double-send race window identified in Phase 2 audit
- Rename sendWelcomeViaBrevo → sendWelcomeViaResend
- Fix 3 hardcoded GH Pages URLs (lines ~234, ~541, ~600) → mva-globalfret.com fallback
- Add wrangler.toml: KV binding placeholder, no [triggers] cron, secrets list
- Update DEPLOIEMENT.md: env vars list (Resend in, Brevo+EmailJS out)
DO NOT MERGE until new Cloudflare account + Worker deployment Phase D ready
(merge écarterait l'ancien Worker Melissa actif si on revenait dessus).
Refs: WordPress → static migration plan, Phase B PR #3a.