v0.4.0 — GnRepeater, redesigned checkbox/radio ...

- Add GnRepeater Vue component for dynamic field groups
- Redesign checkbox and radio styles to match kit aesthetic:
  hard-panel background, accent borders, checkmark/dot indicators,
  hover → primary border, checked → subtle tint + colored mark
- Bump version to 0.4.0

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

Fix Vue demo visual issues and expand component showcase ...

- _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>

Fix Vue demo: dark theme, label color, expanded component showcase ...

- demo/vue.html: replace broken CSS custom properties with real kit colors
  (body background #16161E, text #C0CAF5)
- demo/vue.html: update Vue CDN to 3.5.13
- demo/vue.html: expand demo to show 30+ components including
  Drawer, ConfirmDialog, Navigation, Progress, Timeline, Data Display,
  Identity, Chips, Toolbar, Overlays, EmptyState, Skeleton, Toasts
- _forms.scss: add color: $color-text-light to .label so labels are
  readable on dark backgrounds
- Add toast interaction demo buttons

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

Add date time form controls

Add file upload previews

Expand typography and forms

Add terminal motion interactions

Modernize Sass build pipeline

Scaffold GNexus UI kit