fix(landing): menu mobile funcional + nav branca solida ao rolar

- adiciona painel de menu mobile (sanduiche nao abria nada)
- nav fica branca SOLIDA ao rolar/abrir menu (era bg-white/80 translucido)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/views/LandingPage.tsx

@@ -50,7 +50,7 @@ export const LandingPage: React.FC<{
     return (
         <div className="min-h-screen bg-[#F8FAFC] font-sans selection:bg-blue-100 selection:text-blue-900 overflow-x-hidden">
             {/* Navigation */}
-            <nav className={`fixed top-0 left-0 right-0 z-[100] transition-all duration-500 ${scrolled ? 'bg-white/80 backdrop-blur-xl border-b border-gray-100 py-3 shadow-sm' : 'bg-transparent py-6'}`}>
+            <nav className={`fixed top-0 left-0 right-0 z-[100] transition-all duration-300 ${(scrolled || mobileMenuOpen) ? 'bg-white border-b border-gray-100 py-3 shadow-sm' : 'bg-transparent py-6'}`}>
                 <div className="max-w-7xl mx-auto px-6 flex justify-between items-center">
                     <div className="flex items-center gap-2">
                         <div className="w-10 h-10 bg-gradient-to-tr from-blue-600 to-indigo-600 rounded-xl flex items-center justify-center shadow-lg shadow-blue-200">
@@ -101,6 +101,24 @@ export const LandingPage: React.FC<{
                         </button>
                     </div>
                 </div>
+
+                {/* Menu mobile */}
+                {mobileMenuOpen && (
+                    <div className="md:hidden bg-white border-t border-gray-100 px-6 py-3 mt-3 shadow-lg">
+                        {['features', 'solutions', 'mobile'].map((id, i) => (
+                            <a key={id} href={`#${id}`} onClick={() => setMobileMenuOpen(false)}
+                                className="block py-3 text-sm font-bold text-gray-700 hover:text-blue-600 uppercase tracking-widest border-b border-gray-50">
+                                {['Recursos', 'Soluções', 'Mobile'][i]}
+                            </a>
+                        ))}
+                        <button
+                            onClick={() => { setMobileMenuOpen(false); (isAuthenticated ? onGoToArea : onGetStarted)(); }}
+                            className="w-full mt-3 bg-gray-900 text-white py-3 rounded-full text-xs font-black uppercase tracking-widest hover:bg-blue-600 transition-all active:scale-95"
+                        >
+                            {isAuthenticated ? `Minha área — ${firstName}` : 'Começar Agora'}
+                        </button>
+                    </div>
+                )}
             </nav>
 
             {/* Hero Section */}