Body step 2.1: climbing, mantling, crawling, legs, playground, 144 Hz

- Step rule + lower-body collider: no walking onto tables, steps <= 0.35 m
- Structural hand strength: two-hand mantle/pull-up works, one hand can't
- Arms aim from the physical shoulder horizontally, keep True Body pose vertically
- Crawl pose, crawl carry, 35 deg slope limit, ground feed-forward ignores
  play-space corrections (fixes a runaway feedback loop)
- Grab static world (climbing), procedural visual legs
- Playground sandbox; menu strength slider, spectator (old drag) and turn toggles
- Physics 144 Hz with interpolation; legacy chase-body spikes pin 90 Hz
- RagdollSpike: 27 phases incl. mantle, pull-up, crawl, ledge drop, ramps

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

scripts/Main.cs

@@ -14,6 +14,8 @@ public partial class Main : Node3D
     [Export]
     public int MaximumRefreshRate { get; set; } = 90;
 
+    public const int PhysicsRate = 144;
+
     private OpenXRInterface _xrInterface;
     private bool _xrIsFocused;
 
@@ -70,7 +72,10 @@ public partial class Main : Node3D
             currentRefreshRate = newRate;
         }
 
-        Engine.PhysicsTicksPerSecond = (int)currentRefreshRate;
+        // Physics runs at a fixed PhysicsRate (the ragdoll's joints like small steps), decoupled from
+        // the display; physics interpolation smooths rendering (XR origin subtree excluded — the
+        // runtime and locomotion place it every frame).
+        Engine.PhysicsTicksPerSecond = PhysicsRate;
     }
 
     private void OnSessionVisible()