Add the cockpit seat and hand steering to the Quest launcher

The Quest launcher's Settings > VR gains a Seat choice (cockpit or
custom, first_person_seat) and a Hand steering switch (hand_steering, off
by default like the runtime), which is only enabled in the first-person
cockpit because the wheel belongs to that seat. About credits heurazy for
the turning steering wheel and hand steering. The runtime side was already
shared with the Quest build.

OPENXR.md records what one Quest 3 race showed: the kart's own wheel
animated (228 draws a frame) with the race camera's view matching the
scene's exactly, but the driver's eye was never calibrated and the
fallback put the wheel centre about 13 cm above eye level. The Quest
declares no hand-tracking permission, so hands are the procedural gloves.

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

docs/quest-port.md

@@ -183,7 +183,8 @@ a 2D Horizon OS panel modelled on the PC launcher, WheelWizard VR, and using its
 palette. **Home** has the Play button and reports a missing or incomplete `DATA`
 (the check is the runtime's own `IsDvdDataRoot`: `files/` and `sys/fst.bin`).
 **Settings** edits `Config.toml` in tabs: VR (camera, rotation, driver hiding,
-lean back, render scale, VR interpolation, virtual screen size and distance),
+seat, hand steering, lean back, render scale, VR interpolation, virtual screen
+size and distance),
 Graphics (resolution, widescreen, bloom, shader stutter), Controls (controller
 mode, vibration, the Wii Remote mapping), Audio, and About (paths, OpenXR
 logging). The launch-time geometry (`render_scale`, `hud_distance_meters`,