Completes the basic form controls of W1: a SpinBox reusing SliderModel for
range/step/clamping with an editable_text field (enter/blur commits,
escape reverts, invalid input rejected) and up/down buttons; a CheckBox with
optional tri-state and request-only Toggled events; a RadioGroup that emits
Selected requests. All three follow the request-only contract: the host
applies changes and updates the widget's display state. 45 tests pass.
Mike-Solar
b65ccf1417