c5d89e740c
Add FrameTag.hands (=4) and FrameTag.face (=5) without renumbering existing tags. Implement HandsPayload (up to 255 hands, 21 SIMD3 points each, big-endian codec) and FacePayload (confidence + N SIMD2 landmarks). Both follow the SkeletonPayload/VideoPayload codec pattern. Five new XCTest round-trip and rejection tests pass.