fix(avlivebody): track hand face depth to pelvis

Drive HandFaceSkeleton.setDepth() from the body pelvis z each frame
(negated ARKit→RealityKit) so hand/face markers follow body depth
instead of rendering at the fixed default plane depth 0.

avlivebody-mac/Sources/AVLiveBody/AVLiveBodyApp.swift

@@ -105,7 +105,9 @@ struct ContentView: View {
                                  hands: consumer.hands,
                                  face: consumer.face,
                                  prevPelvis: &prevPelvis)
-        controller.updateHandFace(hands: consumer.hands, face: consumer.face)
+        controller.updateHandFace(hands: consumer.hands,
+                                  face: consumer.face,
+                                  depth: Float(-(prevPelvis?.z ?? 0)))
     }
 
     private func wire() {

avlivebody-mac/Sources/AVLiveBody/SceneController.swift

@@ -95,7 +95,9 @@ final class SceneController {
         mesh?.update(persons)
     }
 
-    func updateHandFace(hands: HandsPayload?, face: FacePayload?) {
+    func updateHandFace(hands: HandsPayload?, face: FacePayload?,
+                        depth: Float) {
+        handFace?.setDepth(depth)
         handFace?.update(hands: hands, face: face)
     }