navigator.credentials.create()/.get() have no platform authenticator to
resolve against in headless Chromium, so passkey/WebAuthn flows hang or
reject outright. `webauthn [on|off]` attaches a CDP virtual authenticator
(ctap2, resident keys, automatic presence simulation) to the active tab,
scoped to the page's lifetime via the existing getOrCreateCdpSession cache.
Bumps VERSION to 1.60.2.0 (patch) and documents the command in
browse/SKILL.md.tmpl (regenerated) and gstack/llms.txt.
Hakim Raja