fix(vehicle): author wheel axles horizontally; record reverse is not the axle

Wheel axles were vertical in Unreal (the FBX armature conversion rolled them 90 deg
about X). Fix: axis_forward:X in the character preset and a Blender-Z wheel tail so the
axle lands on Unreal Y. This is correct (reference pose FL roll 180 / FR roll 0) but
does not fix the reverse: -drivetest still -2737 cm/s, and FinalRatio sign is a no-op.
The remaining cause is the Chaos wheel spin-axis convention or engine torque sign.

MEMORY.md

@@ -1092,3 +1092,16 @@ Historical task context from 2026-11-09/10; later vehicle findings above may sup
   fix** — rotate each wheel bone's reference pose −90° about X in `ue_vehicle_import.py`
   (or a commandlet) so the axle lands on Y. Verify with the `get_ref_bone_pose` probe
   (axle should read ±Y) before re-running `-drivetest`.
+
+## 2026-11-10 — Vehicle reverse: not the axle, not the gear ratio
+
+- The reverse direction is **not** the axle orientation and **not** the final-drive ratio:
+  flipping the wheel-bone axle to horizontal (Unreal ±Y, via `axis_forward: X` + a Blender-Z
+  tail) changed the reference pose (FL roll 180, FR roll 0) but the `-drivetest` still reads
+  `speed=-2737 cm/s`. `FinalRatio = -3.5` also changed nothing (it is a magnitude; the gear
+  direction is `ForwardGearRatios` vs `ReverseGearRatios`).
+- So the wheels spin backward for positive torque regardless of axle direction, which points
+  at the **wheel spin axis convention in the Chaos solver** (the `FSimpleWheel` angular
+  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.