perf(search): release derived caches when track results change

Clear cached buckets, sorted results and history lookups when the source track list changes. This releases the previous search even when empty, loading or error branches skip building results.

lib/screens/home_tab.dart

@@ -361,6 +361,14 @@ class _HomeTabState extends ConsumerState<HomeTab>
   }
 
   void _onTrackStateChanged(TrackState? previous, TrackState next) {
+    if (!identical(previous?.tracks, next.tracks)) {
+      // Home stays alive across tabs. Empty/loading/error branches can skip
+      // result building, so release the previous search's derived lists here.
+      _searchBucketsSourceTracks = null;
+      _searchBucketsCache = null;
+      _invalidateSearchSortCaches();
+      _historySnapshot.update(const []);
+    }
     if (previous != null &&
         !next.hasContent &&
         !next.hasSearchText &&