actions: Add markNarrowAsRead dialog to KeywordSearchNarrow view

Author: chungwwei

lib/widgets/actions.dart

@@ -32,7 +32,8 @@ abstract final class ZulipAction {
   static Future<void> markNarrowAsRead(BuildContext context, Narrow narrow) async {
     final zulipLocalizations = ZulipLocalizations.of(context);
 
-    if (narrow is CombinedFeedNarrow || narrow is ChannelNarrow || narrow is MentionsNarrow) {
+    if (narrow is CombinedFeedNarrow || narrow is ChannelNarrow ||
+      narrow is MentionsNarrow || narrow is KeywordSearchNarrow) {
       final didConfirm = showSuggestedActionDialog(context: context,
         title: zulipLocalizations.markAllAsReadConfirmationDialogTitle,
         message: zulipLocalizations.markAllAsReadConfirmationDialogMessage,