UI Resizable

Two panels split by a draggable handle, where the split ratio is a numeric channel plus a handle idle/hover/press channel (dual-channel value-channel deviation). The Resizable renderer is pure (clamped 0–1 ratio, handle scale, grab-ring opacity); useResizableTransition reads the frame and eases both channels — ratio as a numeric lerp, the handle visual from its state presets. Horizontal and vertical splits; 1px divider + centered grip pill with a derived grab ring.