refactored direct chat logic into a shared utility, implemented direct message shortcuts in the participant list and message reactions, and added reaction visibility checks in the message options dialog

lib/view/pages/talk/details/chat_info.dart

@@ -77,7 +77,10 @@ class _ChatInfoState extends State<ChatInfo> {
                 trailing: const Icon(Icons.arrow_right),
                 onTap: () => TalkNavigator.pushSplitView(
                   context,
-                  ParticipantsListView(participants!),
+                  ParticipantsListView(
+                    participants!,
+                    showDirectMessageAction: isGroup,
+                  ),
                 ),
               ),
             ],