Pose the cockpit hands from the headset's hand tracking

- New [vr] hand_tracking (default off, Quest only for now): the Quest launcher's Settings > VR and
  the headset panel's VR tab, under hand steering. Two XR_EXT_hand_tracking trackers are located
  every XR frame: with the controllers held the Quest builds the joints from their touch sensors
  (XR_EXT_hand_tracking_data_source's controller source), once they are put down from its
  cameras. The trackers exist only while the option and hand steering are on and also serve the
  runtime hand mesh; the extensions (plus XR_FB_hand_tracking_aim) are asked for when either is
  on at launch.
- Aurora skins the runtime mesh with the joints themselves (tracked pose times inverse bind pose,
  no curl, no grip); runtimes with joints but no mesh get a skeleton; non-finite joints put only
  that hand back on its grip curl. AuroraCockpitHand carries the 26 seated-frame joints and radii.
- The manifest declares horizonos.permission.HAND_TRACKING (and the deprecated
  com.oculus.permission.HAND_TRACKING), both normal permissions with no prompt on a Quest 3, and
  oculus.software.handtracking as optional; without it Horizon OS keeps the app controllers-only.
  Bare hands then drive khr/simple_controller, so on Android a hand whose squeeze action is
  inactive and select active is treated as bare: with the option off it presses nothing but the
  menu gesture, is not drawn and feeds no Wii Remote motion.
- Interaction-profile changes and tracker sources are logged. The pure rules (grasp from finger
  flexion, bare latch, pinch gate, bare-hand buttons, flick) live in the OpenXR-free
  vr/openxr_hand_tracking.h with mkw_vr_hand_tracking_tests; the driving and flick parts are
  wired in the next commits. Docs: OPENXR.md, docs/quest-port.md, README.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/quest-port.md

@@ -196,6 +196,23 @@ shoulders, thumbsticks → sticks (clicks → stick buttons), left menu → Star
 and every existing binding, dead zone and overlay setting applies. Bindings are
 suggested for `oculus/touch_controller` and `khr/simple_controller`.
 
+The manifest declares hand tracking (`horizonos.permission.HAND_TRACKING`, the
+deprecated `com.oculus.permission.HAND_TRACKING` for older builds, and
+`oculus.software.handtracking` as optional). Both permissions are `normal` on a
+Quest 3 (`adb shell pm list permissions -g -f`), so there is no prompt. Without
+the feature flag Horizon OS keeps the app controllers-only: the game process logs
+`setting hand mode control settings to ControllersOnly` / `sethandmanifest 0`,
+and putting the controllers down logs `going to controller mode because hands are
+disabled by manifest flag`; with it, `Is hands or controller` /
+`sethandmanifest 2`. Bare hands then drive `khr/simple_controller` (a pinch is
+select, the left palm-up pinch the menu), which the runtime ignores apart from
+the menu gesture unless `[vr] hand_tracking` is on; see "Tracked hands" in
+`OPENXR.md`. The Quest 3 runtime (`libvrapiimpl.so` in the `com.meta.xr` APEX's
+VrDriver.apk) implements `XR_EXT_hand_tracking_data_source`,
+`XR_FB_hand_tracking_aim`, `XR_EXT_hand_interaction`, microgestures and the
+wide-motion modes; Meta's manifest filter skips the wide-motion modes unless the
+app also declares `com.oculus.software.body_tracking`.
+
 ### Android platform glue
 
 - `runtime/src/vr/openxr_android.cpp`: `xrInitializeLoaderKHR` with the
@@ -273,8 +290,8 @@ 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 (race view: immersive, immersive window or flat
 screen, camera, rotation, driver hiding,
-seat, hand steering, lean back, render scale, VR interpolation, virtual screen
-size and distance),
+seat, hand steering, tracked hands, 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`,