perf: optimize scrolling and image loading performance

Added performance optimizations to all library browser views:

- Added cacheExtent: 500 to all GridView/ListView builders to pre-render
  items and reduce stuttering during scrolling
- Wrapped grid items in RepaintBoundary to isolate repaints and improve
  performance
- Optimized CachedNetworkImage with:
  - fadeInDuration/fadeOutDuration: Duration.zero to remove animation overhead
  - memCacheHeight: 300 to limit in-memory cache size
  - maxHeightDiskCache: 600 to resize images for better performance

These changes should significantly reduce the stuttering observed when
scrolling the authors grid and filtering books, especially on first load.

lib/features/library_browser/view/library_genres_page.dart

@@ -29,6 +29,7 @@ class LibraryGenresPage extends HookConsumerWidget {
 
           return ListView.builder(
             padding: const EdgeInsets.symmetric(vertical: 8),
+            cacheExtent: 500,  // Pre-render items for smoother scrolling
             itemCount: sortedGenres.length,
             itemBuilder: (context, index) {
               final genre = sortedGenres[index];