Add macOS support and CI

src/macos_titlebar.h

@@ -0,0 +1,13 @@
+#pragma once
+
+#include <QWidget>
+
+namespace rcx {
+
+struct Theme;
+
+// Apply macOS native title bar color to match the theme.
+// No-op on non-macOS platforms (implementation is platform-specific).
+void applyMacTitleBarTheme(QWidget* window, const Theme& theme);
+
+} // namespace rcx