Fix stale unread badge when message arrives during active conversation

refreshUI() detected and displayed new messages but never called
markRead() or updated the tab badge. Now marks conversation as read
and refreshes the badge whenever new messages are loaded while the
user is actively viewing the conversation.

src/ui/screens/LvMessageView.cpp

@@ -161,6 +161,9 @@ void LvMessageView::refreshUI() {
         _cachedMsgs = std::move(newMsgs);
         _lastMsgCount = (int)_cachedMsgs.size();
         rebuildMessages();
+        // Mark as read since user is actively viewing this conversation
+        _lxmf->markRead(_peerHex);
+        if (_ui) _ui->lvTabBar().setUnreadCount(LvTabBar::TAB_MSGS, _lxmf->unreadCount());
     }
 }