feat(macos): expose WebView and tray lifecycle

[birdmanmandbir]

Summary

• expose the Apple WebView host bridge and external URL opening
• add a Darwin Tray adapter backed by AppKit.StatusItem
• validate menu mutations before native calls and fail clearly when the app-kit capability is absent
• reject NUL-bearing native menu strings before mutation and guard late selection after destroy
• add an explicit unsupported Tray adapter for other platforms
• forward macOS close-to-hide, hide, and show window behavior

Required app-kit StatusItem/runtime capability: tta-lab/bare-app-kit commit f206059.

Verification

• npm test: 10 tests, 39 assertions
• npm run lint
• adapter tests cover invalid mutations, late selection, capability present/absent with fresh window/WebView imports, unsupported platforms, destruction, and terminal close after red-close hiding