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/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>
+  )
+}