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/ListForm.tsx

@@ -3,6 +3,7 @@
 import { useState } from 'react'
 import { createList, updateList } from '@/lib/actions'
 import { useRouter } from 'next/navigation'
+import { useToast } from './ToastContainer'
 
 interface ListFormProps {
   list?: {
@@ -27,6 +28,7 @@ const PRESET_COLORS = [
 
 export default function ListForm({ list, onCancel, onSuccess }: ListFormProps) {
   const router = useRouter()
+  const { showToast } = useToast()
   const [title, setTitle] = useState(list?.title || '')
   const [color, setColor] = useState(list?.color || PRESET_COLORS[0])
   const [isSubmitting, setIsSubmitting] = useState(false)
@@ -47,9 +49,11 @@ export default function ListForm({ list, onCancel, onSuccess }: ListFormProps) {
       if (list) {
         // Update existing list
         await updateList(list.id, { title: title.trim(), color })
+        showToast('List updated successfully', 'success')
       } else {
         // Create new list
         await createList(title.trim(), color)
+        showToast('List created successfully', 'success')
       }
       
       if (onSuccess) {
@@ -59,6 +63,7 @@ export default function ListForm({ list, onCancel, onSuccess }: ListFormProps) {
       }
     } catch (err) {
       setError('Failed to save list. Please try again.')
+      showToast('Failed to save list', 'error')
       console.error(err)
     } finally {
       setIsSubmitting(false)