SystemPauseMgr and NXArgs are game code

Both link in the game archive, and NXArgs uses game classes such as
GameScene. The engine only calls SystemPauseMgr's virtuals, so it now
goes through ksys::ISystemPauseMgr and no longer includes Game/.

(AI assisted using Claude Fable 5.1 and Claude Opus 5.5)

src/Game/SystemPauseMgr.cpp

@@ -0,0 +1,9 @@
+#include "Game/SystemPauseMgr.h"
+
+namespace uking {
+
+SystemPauseMgr::SystemPauseMgr() = default;
+
+SystemPauseMgr::~SystemPauseMgr() = default;
+
+}  // namespace uking