Add Checkbox, Radio, and Switch components ...

- Add SCSS for checkbox, radio, and switch controls with checked,
  disabled, and focus-visible states.
- Add Vue adapters GnCheckbox, GnRadio, GnRadioGroup, GnSwitch matching
  gnexus-ui-kit API.
- Wire components into plugin and entry exports.
- Add Choice controls demo partial and include it in demo/index.html.
- Extend Vue example app with interactive checkbox/radio/switch usage.
- Update component coverage matrix.

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.

Scaffold vmk-ui-kit build system, docs, and compatibility contract ...

- Add Gulp 5 + esbuild + Sass build pipeline mirroring gnexus-ui-kit
- Add package.json with compatible exports (main, module, vue, css, assets)
- Add Playwright config and smoke test
- Add Vue example project for adapter smoke build
- Add placeholder SCSS tokens, JS entry, and Vue plugin
- Add docs skeleton (getting-started, vue, style-guide, release, coverage)
- Add PROJECT_NOTES.md with agreed decisions and open questions
- Update CLAUDE.md with reference architecture and compatibility requirements

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