Add Input, Badge, Alert components and foundation demos ...

- Add src/scss/components/_forms.scss with input, label, help text,
  and error/success/warning states.
- Add src/scss/components/_badges.scss and _alerts.scss with semantic
  variants and outline/size options.
- Add GnInput, GnBadge, GnAlert Vue adapters mirroring gnexus-ui-kit API.
- Update plugin and entry exports for new components.
- Add demo partials for Typography, Palette, Utilities, Inputs, Badges,
  and Alerts, and include them in demo/index.html.
- Extend Vue example app to render new components.

Implement Button component and Vue adapter ...

- Add src/scss/components/_buttons.scss with Figma-extracted variants,
  sizes (lg/md/sm/xs/xxs), states (disabled, loading), icon support,
  and destructive secondary/tertiary styles.
- Add src/vue/components/GnButton.js and VmkIcon with inline SVG loading.
- Add shared src/vue/utils.js for class/variant/size normalization and
  legacy Phosphor-name mapping.
- Wire GnButton and VmkIcon into the Vue plugin and entry exports.
- Add demo partial for buttons and update demo index page.

Integrate user-provided SVG icon set ...

- Extract Icons_svg.zip into public/assets/icons/svg/ (967 icons).
- Replace stroke="black" and fill="black" with currentColor in all SVGs
  so icons inherit text color.
- Build public/assets/icons/index.json mapping clean names to SVG paths.
- Add src/js/components/icon-helper.js for async inline SVG loading.
- Add src/scss/components/_icons.scss with base icon styles.
- Import icons component styles into kit.scss.

Build, Vue example build, and Playwright smoke test still pass.