Body step 2.4: landing, movable ground, playground fixes

- legs brake landings at 4.5 g; vertical support is a rate-limited servo
  (no launch when stepping onto a mantled ledge)
- ground control pushes back on movable ground (seesaw tips under the player)
- playground hinges use absolute paths (joint paths resolve from the joint)
- big props grabbable via surface query; Reset props keeps playground pieces
- spike: landing, seesaw, playground joints/grab, person-like wall climb

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

scripts/PropGrabber.cs

@@ -214,7 +214,30 @@ public partial class PropGrabber : Node
         nearest = NearestProp(handBody.GlobalPosition, CenterGrabRadius);
         if (nearest != null)
             return nearest;
-        return WorldUnderPalm(palm, handBody.GetWorld3D()) ?? WorldUnderPalm(handBody.GlobalPosition, handBody.GetWorld3D());
+        // Big props (planks, seesaw, boards): their origin is far from the hand — use the surface.
+        World3D world = handBody.GetWorld3D();
+        return BodyUnderPalm(palm, world) ?? BodyUnderPalm(handBody.GlobalPosition, world);
+    }
+
+    // The body whose surface is near the point: a "prop" first, else static world (climbing).
+    public static PhysicsBody3D BodyUnderPalm(Vector3 point, World3D world)
+    {
+        PhysicsShapeQueryParameters3D query = new()
+        {
+            Shape = new SphereShape3D { Radius = WorldGrabRadius },
+            Transform = new Transform3D(Basis.Identity, point),
+            CollisionMask = 1,
+        };
+        StaticBody3D found = null;
+        foreach (Godot.Collections.Dictionary hit in world.DirectSpaceState.IntersectShape(query, 8))
+        {
+            GodotObject o = GodotObject.InstanceFromId((ulong)hit["collider_id"]);
+            if (o is RigidBody3D prop && prop.IsInGroup("prop"))
+                return prop;
+            if (o is StaticBody3D body && !body.IsInGroup(NoGrabGroup))
+                found ??= body;
+        }
+        return found;
     }
 
     // Climbing: any static body near the palm (except the "no_grab" group) can be held.