body_tracker.gd used Meta's raw XR_FB_body_tracking indices but Godot's
XRBodyTracker.get_joint_transform() expects Godot's own enum values.
The OpenXR vendors plugin remaps between them, so e.g. index 16
(Meta RIGHT_ARM_LOWER) was actually returning LEFT_FOOT data in Godot,
explaining why right elbow tracking showed floor-level positions.
Also switches retarget_bridge.py from Euler angle decomposition to IK
solver (Pinocchio/CasADi) with elbow position constraints from body
tracking l_lower/r_lower joints.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
melancholytron