Add turbocharged twin scenario and cross-platform test harness

include/FluidSim/MotorcycleTest.hpp

@@ -0,0 +1,22 @@
+#pragma once
+
+#include "FluidSim/Engine.hpp"
+#include "FluidSim/Vehicle.hpp"
+#include <algorithm>
+
+namespace fluidsim::port {
+// Shared longitudinal load and clutch integration for motorcycle/car presets.
+class MotorcycleTest {
+public:
+    Vehicle vehicle{};
+    float load{}, clutch{1.0f};
+
+protected:
+    void step_motorcycle(Crankshaft& crank, float dt, float maximum_load_torque) {
+        crank.load_torque = std::clamp(load, 0.0f, 1.0f) * maximum_load_torque;
+        vehicle.clutch_input = std::clamp(clutch, 0.0f, 1.0f);
+        crank.step(dt);
+        crank.drivetrain_torque = vehicle.update(crank.omega, crank.inertia, dt);
+    }
+};
+} // namespace fluidsim::port