feat(compare): group contrast visibility L1+L2 (v2.1.0)

feat(ui): English-only product copy and EN Compare vocab

feat(ui): add Amplitude Y point activation height slider and Vector Distance Y baseline slider

feat(ui): add front-facing Analysis view with floating Glassmorphic thread labels and 5-thread vertical stack

feat(visualizer): integrate thread geometry spatial 3D sliders into VectorLabApp