Body step 1: one-time T-pose calibration (prefs.json, forced gate) + True Body solver + shared ArmSolver

- BodyProfile (Winter anthropometry, T-pose: arm = (span - shoulder width)/2 - 1.5 cm) and
  Prefs (gitignored prefs.json next to the executable / project folder in editor builds)
- Calibration node: loads prefs, else head-locked prompt + jitter-proof TPoseDetector; body
  systems wait for BodyProfile.Current; Recalibrate() in group "calibration"; recal rebuilds arms
- ArmSolver: PhysicsArms' elbow solve extracted (behaviour-identical) + min reach |U-F| fix
- TrueBody: derived real-body pose (neck, chest yaw + crouch lean at neck pivot, lagging pelvis,
  moving shoulder girdle with scapulohumeral shrug, arms) + debug skeleton
- PhysicsArms/PhysicsTorso/BodyRig now profile-driven (arm length no longer from head height)
- TrueBodySpike PASS x3; all spikes PASS x3 (arm spike thresholds re-based for correct 0.57 m arms;
  CollapseSpike uses a fixed standing profile)

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

scripts/BodyRig.cs

@@ -18,7 +18,8 @@ public partial class BodyRig : Node3D
     private readonly MeshInstance3D[] _upperArmMeshes = new MeshInstance3D[2];
     private readonly MeshInstance3D[] _forearmMeshes = new MeshInstance3D[2];
 
-    private bool _sized;
+    private float _sizedUpper = -1f;
+    private float _sizedFore = -1f;
     private Basis _yawBasis = Basis.Identity;
 
     public override void _Ready()
@@ -59,9 +60,10 @@ public partial class BodyRig : Node3D
         UpdateYawBasis();
         if (!_arms.Calibrated || _arms.UpperArm(0) == null)
             return;
-        if (!_sized)
+        if (_sizedUpper != _arms.UpperLen || _sizedFore != _arms.ForeLen)
         {
-            _sized = true;
+            _sizedUpper = _arms.UpperLen;
+            _sizedFore = _arms.ForeLen;
             for (int side = 0; side < 2; side++)
             {
                 ((BoxMesh)_upperArmMeshes[side].Mesh).Size = new Vector3(0.07f, _arms.UpperLen, 0.07f);