test(vehicle): the chassis box and the gravity are both innocent

Four more things measured instead of guessed:

  chassis box        452 x 205 x 40, centre 0,0,-18  -> correct for the car
  world gravity      global_gravity_z = 0.0, and the character falls normally
  spawn height       5 m up: the pawn still climbs, so penetration is not the cause
  mass override      SetMassOverrideInKg at 0.5 s never logged

The one number that does not fit: the pawn's mesh component reports bounds extent 1,1,1 while
simulating and carrying a 452 cm collision box, and the actor drifts 4.8 m sideways while climbing
with no input. A body that simulates with correct collision but degenerate bounds is not the body the
movement component is driving, so the next question is which component owns it and whether
CreateVehicle() runs at all.

The pawn is parked again; the diagnostic logging stays (it is the tool that produced this), and the
evidence is in the 'Vehicle physics' task.

Game/GigLine/Source/GigLine/GigLineVehicle.h

@@ -82,5 +82,6 @@ private:
 	FVector DriveStart = FVector::ZeroVector;
 
 	float SettleElapsed = 0.f;
+	bool bMassSet = false;
 	bool bSettleReported = false;
 };