Add the cockpit and hand-steering settings, docs and credits

F10 > VR (and the headset panel) gains a Seat choice (cockpit or custom,
with the cockpit scale or the existing custom sliders), "Turn the steering
wheel", "Use the vehicle's own wheel", "Hand steering (by heurazy)" and its
tuning, plus a line saying which wheel the cockpit found and how many
draws took the animated copy. "Reset first-person defaults" covers the
seat and wheel keys; hand steering keeps its own choice.

OPENXR.md documents the seats and a new "Steering wheel and hand
steering" section, fixes the stale first-person defaults in the sample
configuration, and lists the headset validation still owed. README and
THIRD-PARTY-NOTICES credit heurazy's mario-kart-wii-VR-port (GPL-3.0) and
the references it credits.

README.md

@@ -54,7 +54,9 @@ Windows builds can render through an OpenXR runtime on D3D12, or on Vulkan with
 build, without CPU readback. Menus and
 unsupported scenes appear as a head-locked virtual screen; a validated single-camera race switches
 to immersive stereo rendering. VR is opt-in and falls back to the normal desktop renderer if the
-runtime or headset is unavailable. See [`OPENXR.md`](OPENXR.md) for setup, configuration, and the
+runtime or headset is unavailable. In first person you sit in the cockpit, where the steering wheel
+or handlebar turns with your steering, and optional hand steering by heurazy lets you grab it with
+the tracked controllers and turn it. See [`OPENXR.md`](OPENXR.md) for setup, configuration, and the
 current limitations.
 
 **Music ducking.** 
@@ -234,6 +236,8 @@ All translated output is verified against real hardware behavior and most import
   aurora's Direct3D, Vulkan and OpenGL backends.
 - **[OpenXR](https://www.khronos.org/openxr/)** - the Khronos cross-platform API used by the
   experimental VR renderer.
+- **heurazy** - the VR cockpit's turning steering wheel and hand steering, ported from
+  **[mario-kart-wii-VR-port](https://github.com/heurazy/mario-kart-wii-VR-port)** (GPL-3.0).
 - **[Dolphin Emulator](https://github.com/dolphin-emu/dolphin)** - an invaluable reference for Wii
   hardware behavior during development, plus the source of the free DSP coefficient ROM and the
   unmodified default WiiConnect24 bootstrap tree bundled with the runtime.