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

lib/actions.ts

@@ -525,6 +525,8 @@ export async function getItemsByFilter(
     dueDateRange?: { start: Date | null; end: Date | null }
     sortBy?: 'createdAt' | 'dueDate' | 'priority' | 'title'
     sortOrder?: 'asc' | 'desc'
+    page?: number
+    pageSize?: number
   } = {}
 ) {
   try {
@@ -560,14 +562,26 @@ export async function getItemsByFilter(
       }
     }
 
-    // Fetch items from database
-    const items = await retryOperation(() =>
-      prisma.item.findMany({
-        where: whereClause,
-        include: {
-          list: true,
-        },
-      })
+    // Pagination parameters
+    const page = filters.page || 1
+    const pageSize = filters.pageSize || 50
+    const skip = (page - 1) * pageSize
+
+    // Fetch items from database with pagination
+    const [items, totalCount] = await retryOperation(() =>
+      Promise.all([
+        prisma.item.findMany({
+          where: whereClause,
+          include: {
+            list: true,
+          },
+          skip,
+          take: pageSize,
+        }),
+        prisma.item.count({
+          where: whereClause,
+        }),
+      ])
     )
 
     // Filter by tags (client-side since tags are stored as JSON)
@@ -618,7 +632,16 @@ export async function getItemsByFilter(
       return sortOrder === 'asc' ? comparison : -comparison
     })
 
-    return sortedItems
+    return {
+      items: sortedItems,
+      pagination: {
+        page,
+        pageSize,
+        totalCount,
+        totalPages: Math.ceil(totalCount / pageSize),
+        hasMore: page * pageSize < totalCount,
+      },
+    }
   } catch (error) {
     console.error('Error filtering items:', error)
     throw new Error('Failed to filter items. Please try again.')