- _forms.scss: rename .checkbox to .switch, create proper .checkbox
  for checkbox (square) vs switch (slider) differentiation
- GnSwitch.js: create dedicated switch component using .switch class
- _forms.scss: add .radio-group with flex-wrap gap for radio layouts
- GnRadioGroup.js: add radio-group class to container
- _cards.scss: fix .card-horizontal .card-media sizing with
  max-height, aspect-ratio, and align-self: start
- demo/vue.html: fix steps data (label → title)
- demo/vue.html: fix definition list data (definition → description)
- demo/vue.html: add Accordion, InputGroup demos
- demo/vue.html: add NavigationShell import (component registered)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>