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/FilterPanel.tsx

@@ -1,6 +1,6 @@
 'use client'
 
-import { useState } from 'react'
+import { memo, useState } from 'react'
 import { Filter, X, ChevronDown, ChevronUp } from 'lucide-react'
 
 export interface FilterState {
@@ -19,7 +19,7 @@ interface FilterPanelProps {
   showListScope?: boolean
 }
 
-export default function FilterPanel({ 
+function FilterPanel({ 
   filters, 
   onFiltersChange,
   availableTags = [],
@@ -294,3 +294,5 @@ export default function FilterPanel({
     </div>
   )
 }
+
+export default memo(FilterPanel)