Stabilize actor position when hat changes

Override centerAndScaleModel in ActorRenderer to exclude the hat
part from the bounding box calculation, so switching between hats
of different sizes no longer shifts the body/head position.

src/core/rendering/ActorRenderer.js

@@ -283,6 +283,36 @@ export class ActorRenderer extends BaseRenderer {
         }
     }
 
+    /**
+     * Center and scale the actor, excluding the hat from the bounding box
+     * so that changing hats doesn't shift the actor's position.
+     */
+    centerAndScaleModel(scaleFactor) {
+        if (!this.modelGroup) return;
+
+        const box = new THREE.Box3();
+        for (let i = 0; i < this.partGroups.length; i++) {
+            if (i === 1 || !this.partGroups[i]) continue; // skip hat
+            box.expandByObject(this.partGroups[i]);
+        }
+
+        if (box.isEmpty()) {
+            super.centerAndScaleModel(scaleFactor);
+            return;
+        }
+
+        const center = box.getCenter(new THREE.Vector3());
+        const size = box.getSize(new THREE.Vector3());
+
+        this.modelGroup.position.sub(center);
+
+        const maxDim = Math.max(size.x, size.y, size.z);
+        if (maxDim > 0) {
+            const scale = scaleFactor / maxDim;
+            this.modelGroup.scale.setScalar(scale);
+        }
+    }
+
     /**
      * Apply position/direction/up transform from ActorLOD data.
      * The game uses CalcLocalTransform with direction/up vectors.