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.

Tools/blender/fbx_export_preset.py

@@ -60,6 +60,7 @@ _METRIC = {
 _CHARACTER = dict(
     _METRIC,
     object_types={"ARMATURE", "MESH"},
+    axis_forward="X",
     add_leaf_bones=False,
     path_mode="COPY",
     embed_textures=False,