Add USB steering wheel and pedal support

Ported from heurazy's mario-kart-wii-VR-port. F10 > Controllers > USB
wheel and pedals (also in the headset panel) picks and calibrates the
steering axis and both pedals by moving them, and assigns buttons by
pressing them, over raw SDL joysticks: no per-model table or gamepad
mapping, and separate pedals, reversed axes and combined pedal axes all
calibrate the same way. Settings live in PhysicalWheel.toml beside
Config.toml; heurazy's five-button files load unchanged.

The wheel is player 1's GameCube controller. In a race it owns port 0
(steering on the stick, the accelerator on A, the brake pedal braking then
reversing over A and drift, the paddles on R and L), keeping only the
other source's pause and item aim. In menus it adds only deliberate
presses. It arms once every pedal and button is released, stays neutral
in a race while its setup is incomplete, and nothing is opened until it
is enabled. Optional light rumble follows the game's own, capped at 15 %.

Added here: its confirm, a new back button and the steering device's
first hat (D-pad) work the menus, since our VR controllers default to a
Wii Remote and the wheel needs to navigate on its own. Devices SDL
classifies as wheels are marked in the list.

In the VR cockpit the wheel follows the hardware steering and hand
steering steps aside while it drives. README documents setup and
Logitech notes (G HUB, the G29's PS3 switch, shifter gears as buttons);
not yet tried on a physical wheel.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

OPENXR.md

@@ -386,6 +386,11 @@ holding grip no longer reaches the game (it would press C on the Nunchuk or a sh
 gamepad); the triggers, A and the right stick are unchanged. Releasing both grips gives steering back
 to the stick. The settings panel withholds the wheel like any other input.
 
+**A USB wheel.** With a USB wheel and pedals set up (see the README), the wheel drives the race as
+player 1's GameCube controller. The cockpit's wheel follows its calibrated steering, at the same
+full-lock angle as the stick (`wheel_kart_degrees`, `wheel_bike_degrees`), and hand steering steps
+aside while it drives.
+
 **Hands and the separate wheel.** Hands are drawn while hand steering is on: the runtime's own hand
 mesh where it offers one (`XR_EXT_hand_tracking` and `XR_FB_hand_tracking_mesh`, requested only when
 hand steering is on at launch), otherwise procedural gloves that curl with the squeeze. They and the