Restore AnimatorAvatar fixes from Claude (#18248)

Please see @Popov72 's comment here:
#18234 (comment)

I accidentally removed some of the fixes from Claude, and this PR looks
to restore them. Thank you for your help!

---------

Co-authored-by: gbz <gbz@gbzs-MacBook-Pro.local>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Co-authored-by: local <local@local.local>

Author: 4 people

packages/dev/core/src/Animations/animatorAvatar.ts

@@ -820,29 +820,29 @@ export class AnimatorAvatar {
             }
         } else {
             // No axis provided: assume the vertical axis is the one with the larger difference between the reference and the ground reference transform nodes
-            if (Math.abs(sourceRootGroundReferenceDiff.y) > Math.abs(sourceRootGroundReferenceDiff.x)) {
+            const absX = Math.abs(sourceRootGroundReferenceDiff.x);
+            const absY = Math.abs(sourceRootGroundReferenceDiff.y);
+            const absZ = Math.abs(sourceRootGroundReferenceDiff.z);
+            if (absY > absX && absY >= absZ) {
                 verticalAxis = 1;
-            }
-            if (Math.abs(sourceRootGroundReferenceDiff.z) > Math.abs(sourceRootGroundReferenceDiff.y)) {
+            } else if (absZ > absX && absZ > absY) {
                 verticalAxis = 2;
             }
         }
 
         const targetRootGroundReferenceDiff = targetRootTransformNodeOrBone.getAbsolutePosition().subtract(targetGroundReferenceTransformNodeOrBone.getAbsolutePosition());
 
+        const sourceDiff = verticalAxis === 0 ? sourceRootGroundReferenceDiff.x : verticalAxis === 1 ? sourceRootGroundReferenceDiff.y : sourceRootGroundReferenceDiff.z;
+        const targetDiff = verticalAxis === 0 ? targetRootGroundReferenceDiff.x : verticalAxis === 1 ? targetRootGroundReferenceDiff.y : targetRootGroundReferenceDiff.z;
+
         return {
             verticalAxis,
             sourceRootTransformNode,
             sourceGroundReferenceTransformNode,
             targetRootTransformNodeOrBone,
             targetRootPositionAnimation,
             targetGroundReferenceTransformNodeOrBone,
-            proportionRatio:
-                verticalAxis === 0
-                    ? targetRootGroundReferenceDiff.x / sourceRootGroundReferenceDiff.x
-                    : verticalAxis === 1
-                      ? targetRootGroundReferenceDiff.y / sourceRootGroundReferenceDiff.y
-                      : targetRootGroundReferenceDiff.z / sourceRootGroundReferenceDiff.z,
+            proportionRatio: sourceDiff !== 0 ? targetDiff / sourceDiff : 1.0,
         };
     }