Add FormationPlanner include to game_engine.cpp

Co-authored-by: djeada <[email protected]>

app/core/game_engine.cpp

@@ -64,6 +64,7 @@
 #include "game/systems/cleanup_system.h"
 #include "game/systems/combat_system.h"
 #include "game/systems/command_service.h"
+#include "game/systems/formation_planner.h"
 #include "game/systems/game_state_serializer.h"
 #include "game/systems/global_stats_registry.h"
 #include "game/systems/movement_system.h"