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/DeleteItemButton.tsx

@@ -4,6 +4,7 @@ import { useState } from 'react'
 import { useRouter } from 'next/navigation'
 import { deleteItem } from '@/lib/actions'
 import { Trash2 } from 'lucide-react'
+import { useToast } from './ToastContainer'
 
 interface DeleteItemButtonProps {
   itemId: string
@@ -13,6 +14,7 @@ interface DeleteItemButtonProps {
 
 export default function DeleteItemButton({ itemId, listId, variant = 'full' }: DeleteItemButtonProps) {
   const router = useRouter()
+  const { showToast } = useToast()
   const [isDeleting, setIsDeleting] = useState(false)
   const [showConfirm, setShowConfirm] = useState(false)
 
@@ -22,6 +24,7 @@ export default function DeleteItemButton({ itemId, listId, variant = 'full' }: D
     setIsDeleting(true)
     try {
       await deleteItem(itemId)
+      showToast('Task deleted successfully', 'success')
       if (listId) {
         router.push(`/list/${listId}`)
       } else {
@@ -29,6 +32,7 @@ export default function DeleteItemButton({ itemId, listId, variant = 'full' }: D
       }
     } catch (error) {
       console.error('Error deleting item:', error)
+      showToast('Failed to delete task', 'error')
       setIsDeleting(false)
       setShowConfirm(false)
     }