fix(offline): persist plex watched threshold for offline use

lib/services/offline_watch_sync_service.dart

@@ -52,18 +52,20 @@ class OfflineWatchSyncService extends ChangeNotifier {
   /// Get watched threshold for a server. Cascades:
   /// 1. Plex's fetched server prefs (`/:/prefs`)
   /// 2. Jellyfin's fixed [MediaServerClient.watchedThreshold] (0.9)
-  /// 3. Cached value in SettingsService
+  /// 3. Cached value in SettingsService (mirrored by PlexClient.fetchServerPrefs)
   /// 4. Default 90%
   double getWatchedThreshold(ServerId serverId) {
     final client = _serverManager.getClient(serverId);
     if (client is PlexClient && client.serverPrefs.isNotEmpty) {
-      return client.watchedThresholdPercent / 100.0;
+      return client.watchedThreshold;
     }
     if (client != null && client.backend != MediaBackend.plex) {
       // Jellyfin (and any future neutral backend) — the client exposes a
       // fixed threshold that mirrors the wire-protocol behaviour.
       return client.watchedThreshold;
     }
+    // No client bound (offline) or Plex prefs not loaded yet — use the
+    // mirror written on the last successful prefs fetch.
     final cached = SettingsService.instanceOrNull?.read(SettingsService.watchedThresholdPref(serverId)) ?? 90;
     return cached / 100.0;
   }

lib/services/plex_client.dart

@@ -22,6 +22,7 @@ import '../media/server_capabilities.dart';
 import '../utils/external_ids.dart';
 import 'bif_thumbnail_service.dart';
 import 'download_artwork_helpers.dart';
+import 'settings_service.dart';
 import 'library_query_translator.dart';
 import 'scrub_preview_source.dart';
 import '../utils/media_server_http_client.dart';
@@ -1757,6 +1758,15 @@ class PlexClient
     try {
       final response = await _getWithFailover('/:/prefs');
       _serverPrefs = _parseSettingsMap(response);
+      // Mirror the watched threshold to settings: offline paths resolve it
+      // synchronously with no client bound — see
+      // OfflineWatchSyncService.getWatchedThreshold.
+      unawaited(
+        SettingsService.instanceOrNull?.write(
+          SettingsService.watchedThresholdPref(ServerId(serverId)),
+          watchedThresholdPercent,
+        ),
+      );
     } catch (e) {
       appLogger.d('Failed to fetch server prefs: $e');
     }