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

components/DeleteListButton.tsx

@@ -5,6 +5,7 @@ import { Trash2 } from 'lucide-react'
 import { deleteList } from '@/lib/actions'
 import { useRouter } from 'next/navigation'
 import Modal from './Modal'
+import { useToast } from './ToastContainer'
 
 interface DeleteListButtonProps {
   listId: string
@@ -20,6 +21,7 @@ export default function DeleteListButton({
   redirectAfterDelete = false 
 }: DeleteListButtonProps) {
   const router = useRouter()
+  const { showToast } = useToast()
   const [isConfirmOpen, setIsConfirmOpen] = useState(false)
   const [isDeleting, setIsDeleting] = useState(false)
 
@@ -27,6 +29,7 @@ export default function DeleteListButton({
     setIsDeleting(true)
     try {
       await deleteList(listId)
+      showToast('List deleted successfully', 'success')
       setIsConfirmOpen(false)
       if (redirectAfterDelete) {
         router.push('/')
@@ -35,7 +38,7 @@ export default function DeleteListButton({
       }
     } catch (err) {
       console.error('Failed to delete list:', err)
-      alert('Failed to delete list. Please try again.')
+      showToast('Failed to delete list', 'error')
     } finally {
       setIsDeleting(false)
     }