The old gate ran firefox --headless --screenshot, which renders fine even
when the juggler automation layer is missing from the package — so a binary
Playwright can't actually drive (firefox-8) passed and shipped broken.
Replace it with a real drive gate: a 5-leg matrix that launches each binary
over the juggler pipe on its native runner, loads a page, and round-trips JS
(also asserts navigator.webdriver stays hidden). Headless and no screenshot,
so it stays GPU-free on the hosted runners and needs no proxy or secrets.
Same logic is reusable standalone via verify-assets.yml to drive-test an
existing release's assets without a rebuild.
