feat: implement performance optimizations

- Add database indexes for frequently queried fields (listId, completed, priority, dueDate, createdAt)
- Add compound indexes for common query patterns (listId+completed, listId+priority)
- Implement pagination support in getItemsByFilter with configurable page size (default 50)
- Optimize components with React.memo (ItemCard, ListCard, FilterPanel, SearchBar, SearchResults, EmptyState)
- Configure Next.js for better bundle optimization:
  - Enable optimizePackageImports for lucide-react
  - Enable SWC minification
  - Remove console logs in production (except errors/warnings)
  - Optimize images with AVIF/WebP formats
  - Enable compression
  - Disable production source maps for smaller bundles
- Loading states already implemented to prevent layout shift

Task 18 complete - all performance optimizations implemented

components/ListCard.tsx

@@ -1,7 +1,7 @@
 'use client'
 
+import { memo, useState } from 'react'
 import Link from 'next/link'
-import { useState } from 'react'
 import { Edit2 } from 'lucide-react'
 import Modal from './Modal'
 import ListForm from './ListForm'
@@ -17,7 +17,7 @@ interface List {
   }>
 }
 
-export default function ListCard({ list }: { list: List }) {
+function ListCard({ list }: { list: List }) {
   const [isEditModalOpen, setIsEditModalOpen] = useState(false)
   const completedCount = list.items.filter(item => item.completed).length
   const totalCount = list.items.length
@@ -94,4 +94,6 @@ export default function ListCard({ list }: { list: List }) {
       </Modal>
     </>
   )
-}
+}
+
+export default memo(ListCard)