fix: eliminate pull-to-refresh flicker by holding stale data during re-fetch

lib/providers/news_provider.dart

@@ -71,6 +71,25 @@ class NewsNotifier extends AsyncNotifier<NewsState> {
     );
   }
 
+  /// Re-fetch the first page without clearing state (no flicker).
+  Future<void> refresh() async {
+    final current = state.value;
+    final items = await ref.read(newsApiProvider).getNewsItems(
+          days: 90,
+          limit: _limit,
+          offset: 0,
+          feedId: current?.selectedFeedId,
+        );
+    state = AsyncData(NewsState(
+      items: items,
+      offset: items.length,
+      hasMore: items.length == _limit,
+      loadingMore: false,
+      selectedFeedId: current?.selectedFeedId,
+      reactions: {for (final item in items) item.id: item.reaction},
+    ));
+  }
+
   Future<void> loadMore() async {
     final current = state.value;
     if (current == null || current.loadingMore || !current.hasMore) return;