Implements W1's slider: a pure SliderModel state machine (float, integer,
rational and angle kinds with clamping, step snapping, fine adjustment and
drag math) plus the Slider view with vertical-drag scrubbing (shift for
fine), double-click direct entry backed by editable_text (enter commits,
escape cancels, click-away commits, invalid text rejected), wheel stepping,
middle-click reset and arrow-key navigation. Every edit is emitted as a
SliderEvent request; keyable controls expose a Keying diamond. 37 unit and
interaction tests pass.
Mike-Solar
6e0b541660