docs(vehicle): revert the axis fix; the reverse is in the Chaos solver

The axis_forward:X / Blender-Z axle fix changed the reference pose but not the drive
(-2737 cm/s), and axis_forward:X also alters the shared character preset. Revert it.
The Chaos solver drives the wheel about the vehicle's Y (not the bone), and the
drive force is positive yet the car moves backward - the inversion is in the engine
torque / drive-force sign. Next: GetEngineTorque() sign or a SetupVehicle override.

MEMORY.md

@@ -1105,3 +1105,15 @@ Historical task context from 2026-11-09/10; later vehicle findings above may sup
   velocity axis) or the engine torque sign, not the bone authoring. The horizontal-axle fix
   is kept (it is correct even if insufficient): `axis_forward: X` in the character preset and
   a Blender-Z wheel tail (`r - copysign(0.25, y)`) so the axle lands on Unreal Y.
+
+## 2026-11-10 — Vehicle reverse is in the Chaos solver, not the assets (revert the axis fix)
+
+- Reverted the `axis_forward: X` / Blender-Z axle fix (`ecdd820`): the reference pose changed
+  but `-drivetest` still read −2737 cm/s, and `axis_forward: X` lives in the shared character
+  preset, so it would also alter every character export.
+- Traced the Chaos solver: the wheel's local frame is `GroundXVector = CrossProduct(VehicleRightAxis,
+  GroundZVector)` and the drive force is `FinalLongitudinalForce = DriveTorque / Re`, applied forward —
+  yet the car moves backward. The wheel spins about the **vehicle's** Y, not the bone's, so the bone
+  authoring is irrelevant. The inversion is in the **engine-torque / drive-force sign** (`FSimpleWheel`),
+  not the assets. Next: check `GetEngineTorque()` sign, or override `SetupVehicle`/`ProcessMechanicalSimulation`
+  in `UGigLineVehicleMovement` to negate the drive torque.