fix :: mainwindow.cpp QTimer 헤더 누락 수정

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: BitByte08

apps/cluster/mainwindow.cpp

@@ -11,6 +11,7 @@
 
 #include <QVBoxLayout>
 #include <QProcess>
+#include <QTimer>
 #include <memory>
 
 static constexpr const char *kGithubRepo = "BitByte08/Cockpit.EntertainmentClusterUnit";