fix(site): completely remove Launch Sandbox menu and mockup pages

site/src/sections/Header.tsx

@@ -43,13 +43,6 @@ export function Header() {
               {t.nav[link.key]}
             </a>
           ))}
-          <a
-            href="/launch-readiness.html"
-            className="font-mono text-nano uppercase tracking-widest text-cyan-400 hover:text-cyan-300 transition-colors flex items-center gap-1"
-          >
-            <span className="w-1.5 h-1.5 rounded-full bg-cyan-400 animate-pulse"></span>
-            Launch Sandbox
-          </a>
         </nav>
 
         {/* Right side: language + CTA */}