refactor: centralize globalKey construction via buildGlobalKey()

lib/utils/deletion_notifier.dart

@@ -1,6 +1,7 @@
 import '../models/plex_metadata.dart';
 import 'app_logger.dart';
 import 'base_notifier.dart';
+import 'global_key_utils.dart';
 import 'hierarchical_event_mixin.dart';
 
 /// Event representing a media item deletion with parent chain for hierarchical invalidation
@@ -42,7 +43,7 @@ class DeletionEvent with HierarchicalEventMixin {
     required this.mediaType,
     this.leafCount = 1,
     this.isDownloadOnly = false,
-  }) : globalKey = '$serverId:$ratingKey';
+  }) : globalKey = buildGlobalKey(serverId, ratingKey);
 
   @override
   String toString() => 'DeletionEvent(deleted: $globalKey, type: $mediaType, parents: $parentChain)';

lib/utils/global_key_utils.dart

@@ -1,3 +1,6 @@
+/// Builds a globalKey string from [serverId] and [ratingKey].
+String buildGlobalKey(String serverId, String ratingKey) => '$serverId:$ratingKey';
+
 /// Parses a globalKey string (format: "serverId:ratingKey") into its components.
 ///
 /// Returns `null` if the key does not contain a colon separator.

lib/utils/hierarchical_event_mixin.dart

@@ -1,3 +1,5 @@
+import 'global_key_utils.dart';
+
 /// Mixin providing hierarchical event matching methods.
 ///
 /// Events that represent changes to media items often need to check if they
@@ -24,7 +26,7 @@ mixin HierarchicalEventMixin {
 
   /// Check if this event affects a specific globalKey.
   bool affectsGlobalKey(String globalKey) =>
-      this.globalKey == globalKey || parentChain.any((pk) => '$serverId:$pk' == globalKey);
+      this.globalKey == globalKey || parentChain.any((pk) => buildGlobalKey(serverId, pk) == globalKey);
 
   /// Check if this event affects any item in a collection.
   bool affectsAnyOf(Iterable<String> ratingKeys) => ratingKeys.any(affectsItem);

lib/utils/video_player_navigation.dart

@@ -77,7 +77,7 @@ Future<bool?> navigateToVideoPlayer(
 
       if (isOffline) {
         // Offline mode: resolve local file path for the external player
-        final globalKey = '${metadata.serverId}:${metadata.ratingKey}';
+        final globalKey = metadata.globalKey;
         final videoPath = await downloadProvider.getVideoFilePath(globalKey);
         if (videoPath != null && context.mounted) {
           final videoUrl = videoPath.contains('://') ? videoPath : 'file://$videoPath';

lib/utils/watch_state_notifier.dart

@@ -1,6 +1,7 @@
 import '../models/plex_metadata.dart';
 import 'app_logger.dart';
 import 'base_notifier.dart';
+import 'global_key_utils.dart';
 import 'hierarchical_event_mixin.dart';
 
 /// Types of watch state changes
@@ -47,7 +48,7 @@ class WatchStateEvent with HierarchicalEventMixin {
     required this.mediaType,
     this.viewOffset,
     this.isNowWatched,
-  }) : globalKey = '$serverId:$ratingKey';
+  }) : globalKey = buildGlobalKey(serverId, ratingKey);
 
   @override
   String toString() => 'WatchStateEvent($changeType, $globalKey, parents: $parentChain)';