fix(mobile-menu): transition to global Alpine store for reliable state management

partials/header.hbs

@@ -22,7 +22,7 @@
                 </button>
             </nav>
 
-            <button @click="mobileMenuOpen = true" class="md:hidden p-2 rounded-full bg-[var(--bg-secondary)] text-[var(--text-primary)] hover:bg-[var(--bg-tertiary)] transition-colors duration-200">
+            <button @click="$store.mobileMenu.toggle()" class="md:hidden p-2 rounded-full bg-[var(--bg-secondary)] text-[var(--text-primary)] hover:bg-[var(--bg-tertiary)] transition-colors duration-200">
                 <svg xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 24 24" stroke-width="1.5" stroke="currentColor" class="w-6 h-6">
                     <path stroke-linecap="round" stroke-linejoin="round" d="M3.75 6.75h16.5M3.75 12h16.5m-16.5 5.25h16.5" />
                 </svg>