feat: Add visual feedback and polish (Task 15)

- Implement toast notification system for success/error messages
- Add loading states with skeleton loaders for async operations
- Create smooth CSS transitions and animations
- Enhance empty states with EmptyState component
- Add loading.tsx files for Next.js loading states
- Integrate toast notifications across all CRUD operations
- Add fade-in and scale-in animations for better UX
- Improve visual feedback for user actions

app/layout.tsx

@@ -2,6 +2,7 @@ import type { Metadata } from 'next'
 import './globals.css'
 import ServiceWorkerRegistration from '@/components/ServiceWorkerRegistration'
 import OfflineIndicator from '@/components/OfflineIndicator'
+import { ToastProvider } from '@/components/ToastContainer'
 
 export const metadata: Metadata = {
   title: 'Ultimate Lists',
@@ -67,9 +68,11 @@ export default function RootLayout({
         <meta name="apple-mobile-web-app-status-bar-style" content="black-translucent" />
       </head>
       <body className="bg-gray-50 min-h-screen">
-        <ServiceWorkerRegistration />
-        <OfflineIndicator />
-        {children}
+        <ToastProvider>
+          <ServiceWorkerRegistration />
+          <OfflineIndicator />
+          {children}
+        </ToastProvider>
       </body>
     </html>
   )