perf: limit concurrent image transcode requests

lib/main.dart

@@ -79,7 +79,8 @@ void main() async {
   await initializeDateFormatting(savedLocale.languageCode, null);
 
   // Configure image cache for large libraries
-  PaintingBinding.instance.imageCache.maximumSizeBytes = 200 << 20; // 200MB
+  PaintingBinding.instance.imageCache.maximumSize = 2000; // default 1000
+  PaintingBinding.instance.imageCache.maximumSizeBytes = 300 << 20; // 300MB
 
   // Initialize services in parallel where possible
   final futures = <Future<void>>[];

lib/services/image_cache_service.dart

@@ -0,0 +1,29 @@
+import 'dart:io';
+
+import 'package:flutter_cache_manager/flutter_cache_manager.dart';
+import 'package:http/io_client.dart';
+
+/// Custom cache manager for Plex image transcoding with connection limiting.
+///
+/// Limits concurrent HTTP connections to 6 per host (matching browser HTTP/1.1
+/// behavior) to prevent overwhelming the Plex server's transcode pipeline when
+/// many posters are visible simultaneously.
+class PlexImageCacheManager extends CacheManager with ImageCacheManager {
+  static const _key = 'plexImageCache';
+
+  static final PlexImageCacheManager instance = PlexImageCacheManager._();
+
+  PlexImageCacheManager._()
+      : super(
+          Config(
+            _key,
+            stalePeriod: const Duration(days: 30),
+            maxNrOfCacheObjects: 5000,
+            fileService: HttpFileService(
+              httpClient: IOClient(
+                HttpClient()..maxConnectionsPerHost = 6,
+              ),
+            ),
+          ),
+        );
+}

lib/widgets/plex_optimized_image.dart

@@ -4,6 +4,7 @@ import 'package:flutter/material.dart';
 import 'package:plezy/widgets/app_icon.dart';
 import 'package:material_symbols_icons/symbols.dart';
 import 'package:cached_network_image/cached_network_image.dart';
+import '../services/image_cache_service.dart';
 import '../../services/plex_client.dart';
 import '../utils/plex_image_helper.dart';
 import 'media_card.dart';
@@ -338,6 +339,7 @@ class PlexOptimizedImage extends StatelessWidget {
       image: CachedNetworkImageProvider(
         imageUrl,
         cacheKey: effectiveCacheKey,
+        cacheManager: PlexImageCacheManager.instance,
         headers: const {'User-Agent': 'Plezy'},
         maxHeight: memHeight,
       ),