feat(cloudflare): point HTML/JS to new Mind4Solutions Worker + Turnstile sitekey

Companion change to PR #3a (= Worker code Brevo\xe2\x86\x92Resend on
feat/cloudflare-worker-resend-migration). Updates the 3 client-side
references that point to the previous Cloudflare Worker (Melissa account)
and Turnstile widget, switching them to the fresh Mind4Solutions resources
provisioned in Phase D.

- js/confirmation.js:20 \xe2\x86\x92 mva-hubspot-proxy.sergemind4s.workers.dev
- js/form-handler.js:31 \xe2\x86\x92 mva-hubspot-proxy.sergemind4s.workers.dev
- contact.html:145 \xe2\x86\x92 Turnstile sitekey 0x4AAAAAADKk5L_1GV_IS_s9

Refs: WordPress \xe2\x86\x92 static migration plan, Phase B PR #3b.

contact.html

@@ -142,7 +142,7 @@
               </div>
 
               <!-- Cloudflare Turnstile (CAPTCHA invisible/léger pour bloquer les bots) -->
-              <div class="cf-turnstile" data-sitekey="0x4AAAAAADKDuc7Rmlb1svIL" data-callback="onTurnstileSuccess" data-error-callback="onTurnstileError" style="margin-bottom: 16px;"></div>
+              <div class="cf-turnstile" data-sitekey="0x4AAAAAADKk5L_1GV_IS_s9" data-callback="onTurnstileSuccess" data-error-callback="onTurnstileError" style="margin-bottom: 16px;"></div>
 
               <div id="formErrorGlobal" style="display:none; color: var(--red); margin-bottom: 16px; font-size: 0.9rem;"></div>
 

js/confirmation.js

@@ -17,7 +17,7 @@
 // avec invitation à contacter le support.
 // ============================================================
 
-const WORKER_PROXY_URL = 'https://mva-hubspot-proxy.mvaglobalfret.workers.dev';
+const WORKER_PROXY_URL = 'https://mva-hubspot-proxy.sergemind4s.workers.dev';
 
 document.addEventListener('DOMContentLoaded', async () => {
   const token = new URLSearchParams(window.location.search).get('token');

js/form-handler.js

@@ -28,7 +28,7 @@ if (typeof emailjs !== 'undefined') {
 //   'https://mva-hubspot-proxy.moncompte.workers.dev'
 // Tant que cette constante est vide, la vérification doublon est désactivée
 // (le formulaire s'envoie normalement — aucun blocage).
-const WORKER_PROXY_URL = 'https://mva-hubspot-proxy.mvaglobalfret.workers.dev';
+const WORKER_PROXY_URL = 'https://mva-hubspot-proxy.sergemind4s.workers.dev';
 
 document.addEventListener('DOMContentLoaded', () => {
   const form = document.getElementById('contactForm');