- 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>