perf: shrink semantics tree on media lists

Poster images are decorative (the card exposes one merged node), and
the default per-child AutomaticKeepAlive/_SelectionKeepAlive/
IndexedSemantics wrappers are inert here — no keep-alive clients or
SelectionArea exist. The semantics phase ran ~9ms every frame on TV
devices with an accessibility service; it scales with node count.

lib/screens/libraries/tabs/library_browse_tab.dart

@@ -1741,6 +1741,10 @@ class _LibraryBrowseTabState extends BaseLibraryTabState<MediaItem, LibraryBrows
       return SliverPadding(
         padding: .fromLTRB(8, topPadding, rightPadding, 8),
         sliver: SliverList.builder(
+          // Inert on media lists (no keep-alive clients): dropping the
+          // per-child wrappers shrinks build + semantics work per item.
+          addAutomaticKeepAlives: false,
+          addSemanticIndexes: false,
           itemCount: itemCount,
           itemBuilder: (context, index) {
             final child = _buildMediaCardItem(
@@ -1784,6 +1788,10 @@ class _LibraryBrowseTabState extends BaseLibraryTabState<MediaItem, LibraryBrows
               itemHeight: geometry.itemHeight,
             );
             return SliverGrid.builder(
+              // Inert on media lists (no keep-alive clients): dropping the
+              // per-child wrappers shrinks build + semantics work per item.
+              addAutomaticKeepAlives: false,
+              addSemanticIndexes: false,
               gridDelegate: geometry.delegate,
               itemCount: itemCount,
               itemBuilder: (context, index) => _buildMediaCardItem(

lib/screens/libraries/tabs/library_collections_tab.dart

@@ -139,6 +139,10 @@ class _LibraryCollectionsTabState extends BaseLibraryTabState<MediaItem, Library
     return SliverPadding(
       padding: _effectivePadding,
       sliver: SliverList.builder(
+        // Inert on media lists (no keep-alive clients): dropping the
+        // per-child wrappers shrinks build + semantics work per item.
+        addAutomaticKeepAlives: false,
+        addSemanticIndexes: false,
         itemCount: totalSize,
         itemBuilder: (context, index) =>
             _buildMediaCardItem(index, isFirstRow: index == 0, isFirstColumn: true, disableScale: true),
@@ -158,6 +162,10 @@ class _LibraryCollectionsTabState extends BaseLibraryTabState<MediaItem, Library
             fullBleedImage: fullCardLayout,
           );
           return SliverGrid.builder(
+            // Inert on media lists (no keep-alive clients): dropping the
+            // per-child wrappers shrinks build + semantics work per item.
+            addAutomaticKeepAlives: false,
+            addSemanticIndexes: false,
             gridDelegate: geometry.delegate,
             itemCount: totalSize,
             itemBuilder: (context, index) => _buildMediaCardItem(

lib/screens/libraries/tabs/library_playlists_tab.dart

@@ -141,6 +141,10 @@ class _LibraryPlaylistsTabState extends BaseLibraryTabState<MediaPlaylist, Libra
     return SliverPadding(
       padding: _effectivePadding,
       sliver: SliverList.builder(
+        // Inert on media lists (no keep-alive clients): dropping the
+        // per-child wrappers shrinks build + semantics work per item.
+        addAutomaticKeepAlives: false,
+        addSemanticIndexes: false,
         itemCount: totalSize,
         itemBuilder: (context, index) =>
             _buildPlaylistCard(index, isFirstRow: index == 0, isFirstColumn: true, disableScale: true),
@@ -160,6 +164,10 @@ class _LibraryPlaylistsTabState extends BaseLibraryTabState<MediaPlaylist, Libra
             fullBleedImage: fullCardLayout,
           );
           return SliverGrid.builder(
+            // Inert on media lists (no keep-alive clients): dropping the
+            // per-child wrappers shrinks build + semantics work per item.
+            addAutomaticKeepAlives: false,
+            addSemanticIndexes: false,
             gridDelegate: geometry.delegate,
             itemCount: totalSize,
             itemBuilder: (context, index) => _buildPlaylistCard(