fix: icon mapping for common Phosphor names and toast provider resolution ...

- Map copy, chart-line-up, check-circle, chat-circle, lock-key, sign-in/out,
  pencil, pencil-simple, house, list, credit-card, bell, cloud-arrow-up,
  package, gear, home, login, logout, edit, message, box to real VMK icon keys.
- Use Symbol.for for toastKey so builds with multiple bundles resolve the same key.
- Add globalProperties fallback in useToast/GnToastProvider for inline createApp demos.

Add overlay components: Modal, Drawer, Toast system ...

- Add SCSS for modals, drawers and toasts with VMK design tokens.
- Add GnModal and GnDrawer Vue adapters with focus trap, Escape close and teleport.
- Add browser Toasts helper and GnToastProvider + useToast composable.
- Wire overlays into plugin, Vue entry and browser bundle.
- Add demo partials for Modal, Drawer and Toast.
- Update component coverage and project notes.