fix(browse): keep show in browse after deleting its downloads

The browse grid listens for DeletionEvents and decrements each show's
leafCount, evicting the show when the count hits zero. Download-only
deletions (isDownloadOnly: true) fired one event per episode, so deleting
every downloaded episode of a show drove its leafCount to zero and removed
it from browse - even though the content still exists on the server.

Browse is online-only (the Libraries tab is hidden when offline) and always
reflects server-side content, so it must ignore download-only deletions.
Add a guard at the top of onDeletionEvent, matching the existing
isDownloadOnly contract already honored by media_detail_screen.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/screens/libraries/tabs/library_browse_tab.dart

@@ -153,6 +153,13 @@ class _LibraryBrowseTabState extends BaseLibraryTabState<MediaItem, LibraryBrows
 
   @override
   void onDeletionEvent(DeletionEvent event) {
+    // Browse is online-only (the Libraries tab is hidden when offline), so it
+    // always reflects server-side content. A download-only deletion removes
+    // local files but leaves the item on the server, so it must not affect the
+    // browse grid. Without this guard, deleting every downloaded episode of a
+    // show drives its leafCount to zero and evicts the show from browse.
+    if (event.isDownloadOnly) return;
+
     // If we have an item that matches the rating key exactly, remove it and rebuild indices
     final matchEntry = loadedItems.entries.where((e) => e.value.id == event.itemId).firstOrNull;
     if (matchEntry != null) {