Adds Playwright end-to-end tests covering three targets:
- the demo build
- a new lightweight test app exercising several scenarios (theming,
admin/non-admin sidebar, panel navigation, more-info dialog)
- the component gallery
Includes the gulp/rspack build infra for the test app and an "E2E Tests"
GitHub Actions workflow that builds each target once, shares it via
artifacts, and runs the suites on Chromium and mobile Chrome. Browser
install is cached and retried to avoid intermittent download stalls.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>