test(vehicle): the writer is not in the pawn's tick

Sampled the actor transform immediately before and after Super::Tick on every frame: it never changes
there. The 'inside Super::Tick' line never fires, yet the actor climbs 400-1400 cm/s.

With the earlier results that leaves exactly one consistent candidate: the Chaos movement component's own
tick or its async physics step, outside APawn::Tick. That also explains why SetComponentTickEnabled(false)
did not stop the climb and why the body's reported velocity is ~0 while the actor moves - the movement
component is writing a transform it took from a vehicle state that was never created.

Next step is a subclass of UChaosWheeledVehicleMovementComponent that logs UpdateState /
OnUpdateTransform together with the vehicle-state pointer, so the write is caught at its source rather
than inferred from the actor.

Game/GigLine/Source/GigLine/GigLineVehicle.cpp

@@ -265,8 +265,27 @@ void AGigLineVehicle::BeginPlay()
 
 void AGigLineVehicle::Tick(float DeltaSeconds)
 {
+	// Which writer moves the actor? Sample the transform before and after the base class tick:
+	// a change between the two happened inside APawn::Tick (movement component, attachment
+	// update, animation), a change between this frame's exit and the next frame's entry came
+	// from somewhere else entirely.
+	const FVector BeforeSuper = GetActorLocation();
+
 	Super::Tick(DeltaSeconds);
 
+	const FVector AfterSuper = GetActorLocation();
+	if (!AfterSuper.Equals(BeforeSuper, 1.0))
+	{
+		static float LoggedThisPhase = -1.0f;
+		if (SettleElapsed - LoggedThisPhase > 0.25f)
+		{
+			LoggedThisPhase = SettleElapsed;
+			UE_LOG(LogTemp, Warning,
+				TEXT("GigLine vehicle writer: inside Super::Tick %.0f -> %.0f (dz %.0f)"),
+				BeforeSuper.Z, AfterSuper.Z, AfterSuper.Z - BeforeSuper.Z);
+		}
+	}
+
 	// One settled-state report: proves the physics body exists, is simulating, and has
 	// come to rest on the road rather than falling through it. Everything else about the
 	// driving behaviour is measured later; this is the "is it real" check.