feat(i18n): send current language in waitlist form POST body

index.html

@@ -1156,6 +1156,7 @@
         <circle cx="32" cy="32" r="2.5" fill="#040404" opacity="0.18"/>
       </svg><span>adiuv<span class="ai">AI</span></span>
     </a>
+    <div class="nav-right">
       <details id="lang-dropdown" class="lang-switcher">
         <summary class="lang-current" aria-label="Select language"><i data-lucide="globe" style="width:16px;height:16px;"></i> <span id="lang-current-label">EN</span></summary>
         <div class="lang-options">
@@ -1167,6 +1168,7 @@
         </div>
       </details>
       <a href="#final-cta" class="btn btn-primary" data-i18n="navJoinWaitlist">Join the waitlist</a>
+    </div>
   </nav>
 
   <!-- ═══════ HERO ═══════ -->
@@ -1674,7 +1676,7 @@
         const res = await fetch('/api/v1/waitlist', {
           method: 'POST',
           headers: { 'Content-Type': 'application/json' },
-          body: JSON.stringify({ email }),
+          body: JSON.stringify({ email, lang }),
         });
 
         if (!res.ok) throw new Error(res.statusText);