- Create GnLoginCard Vue adapter component with username/password
  fields, optional remember-me checkbox, submit button, and
  forgot-password / sign-up links.
- Add `.login-card` styles in _cards.scss with centered header,
  full-width submit button, and spaced link row.
- Register GnLoginCard in plugin and index exports.
- Add login-card demo block to demo/partials/cards.html.
- Update CLAUDE.md, README, and Vue docs with component entry.

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