Add Vue adapter behavior contract tests ...

- vitest + jsdom + @vue/test-utils; 38 tests over utils, GnModal,
  GnToastProvider, GnFileUpload, GnCombobox covering the CLAUDE.md
  behavior contracts (focus trap, a-hide/a-show transition order,
  single-toast replacement, object URL cleanup, combobox ARIA/keyboard)
- wire test:unit into release:check
- fix GnModal never opening when mounted with open=true (watcher had
  no immediate flag; demo only ever toggles open after mount)