Fix V-face deformation with lower-jaw landmark pins; pass regression

docs/verification/v1.3.1/real-pose-asan.txt

@@ -0,0 +1,2 @@
+2026-10-22 16:25:35.195 slim-tests[22704:8027100] FBBA: creating VNFaceBBoxAligner from VNFaceDetectorRevision2: VNFaceDetectorRevision2
+PASS: 1561 slim alignment checks; maximum UV oracle error 1.09828022e-05