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/globals.css

@@ -30,6 +30,57 @@ mark {
   }
 }
 
+/* Animations for visual feedback */
+@layer utilities {
+  @keyframes slide-in-right {
+    from {
+      transform: translateX(100%);
+      opacity: 0;
+    }
+    to {
+      transform: translateX(0);
+      opacity: 1;
+    }
+  }
+  
+  @keyframes fade-in {
+    from {
+      opacity: 0;
+    }
+    to {
+      opacity: 1;
+    }
+  }
+  
+  @keyframes scale-in {
+    from {
+      transform: scale(0.95);
+      opacity: 0;
+    }
+    to {
+      transform: scale(1);
+      opacity: 1;
+    }
+  }
+  
+  .animate-slide-in-right {
+    animation: slide-in-right 0.3s ease-out;
+  }
+  
+  .animate-fade-in {
+    animation: fade-in 0.2s ease-out;
+  }
+  
+  .animate-scale-in {
+    animation: scale-in 0.2s ease-out;
+  }
+  
+  /* Smooth transitions for interactive elements */
+  .transition-smooth {
+    transition: all 0.2s ease-in-out;
+  }
+}
+
 /* Smooth scrolling for better mobile experience */
 @layer base {
   html {

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>
   )

app/list/[id]/loading.tsx

@@ -0,0 +1,35 @@
+import { ListDetailSkeleton } from '@/components/SkeletonLoader'
+import { ArrowLeft } from 'lucide-react'
+import Link from 'next/link'
+
+export default function Loading() {
+  return (
+    <main className="container mx-auto px-4 sm:px-6 py-6 sm:py-8 max-w-6xl">
+      {/* Header Skeleton */}
+      <div className="mb-6 sm:mb-8">
+        <Link 
+          href="/" 
+          className="inline-flex items-center gap-2 text-gray-600 hover:text-gray-900 mb-4 transition-colors tap-target-sm text-sm sm:text-base"
+        >
+          <ArrowLeft size={20} className="flex-shrink-0" />
+          <span>Back to Lists</span>
+        </Link>
+        
+        <div className="flex items-center gap-2 sm:gap-3 mb-2">
+          <div className="w-5 h-5 sm:w-6 sm:h-6 rounded-full bg-gray-200 animate-pulse" />
+          <div className="h-8 sm:h-10 w-48 bg-gray-200 rounded animate-pulse" />
+        </div>
+        
+        <div className="h-5 w-32 bg-gray-200 rounded animate-pulse" />
+      </div>
+
+      {/* Inline Item Creation Skeleton */}
+      <div className="mb-6 sm:mb-8">
+        <div className="h-14 bg-gray-100 border-2 border-dashed border-gray-300 rounded-lg animate-pulse" />
+      </div>
+
+      {/* Items List Skeleton */}
+      <ListDetailSkeleton />
+    </main>
+  )
+}

app/loading.tsx

@@ -0,0 +1,24 @@
+import { ListCardSkeleton } from '@/components/SkeletonLoader'
+
+export default function Loading() {
+  return (
+    <main className="container mx-auto px-4 sm:px-6 py-6 sm:py-8 max-w-7xl">
+      <div className="flex flex-col sm:flex-row items-start sm:items-center justify-between gap-4 mb-6 sm:mb-8">
+        <div className="h-10 w-48 bg-gray-200 rounded animate-pulse" />
+        <div className="h-12 w-32 bg-gray-200 rounded-lg animate-pulse" />
+      </div>
+
+      {/* Global Search Skeleton */}
+      <div className="mb-6 sm:mb-8">
+        <div className="h-12 bg-gray-100 border border-gray-300 rounded-lg animate-pulse" />
+      </div>
+
+      <div className="grid grid-cols-1 sm:grid-cols-2 lg:grid-cols-3 xl:grid-cols-4 gap-4 sm:gap-6">
+        <ListCardSkeleton />
+        <ListCardSkeleton />
+        <ListCardSkeleton />
+        <ListCardSkeleton />
+      </div>
+    </main>
+  )
+}

app/page.tsx

@@ -2,6 +2,7 @@ import { getLists } from '@/lib/actions'
 import ListCard from '@/components/ListCard'
 import NewListButton from '@/components/NewListButton'
 import GlobalSearch from '@/components/GlobalSearch'
+import EmptyState from '@/components/EmptyState'
 
 export default async function Home() {
   const lists = await getLists()
@@ -18,16 +19,18 @@ export default async function Home() {
         <GlobalSearch />
       </div>
 
-      <div className="grid grid-cols-1 sm:grid-cols-2 lg:grid-cols-3 xl:grid-cols-4 gap-4 sm:gap-6">
-        {lists.map((list) => (
-          <ListCard key={list.id} list={list} />
-        ))}
-      </div>
-
-      {lists.length === 0 && (
-        <div className="text-center py-12 sm:py-16">
-          <p className="text-gray-500 text-base sm:text-lg mb-3 sm:mb-4">No lists yet</p>
-          <p className="text-gray-400 text-sm sm:text-base">Create your first list to get started</p>
+      {lists.length === 0 ? (
+        <EmptyState
+          icon="list"
+          title="No lists yet"
+          description="Create your first list to start organizing your tasks"
+          action={<NewListButton />}
+        />
+      ) : (
+        <div className="grid grid-cols-1 sm:grid-cols-2 lg:grid-cols-3 xl:grid-cols-4 gap-4 sm:gap-6 animate-fade-in">
+          {lists.map((list) => (
+            <ListCard key={list.id} list={list} />
+          ))}
         </div>
       )}
     </main>