The bare `request` fixture is an isolated API context that does not
share the browser session cookie established by login(). Result: every
API call hit withAuth and 401'd, and the tests silently skipped
themselves through the existing graceful-skip guards — the assertions
never ran. Switching to page.request shares the browser context cookie
jar, so the API calls now reach the handler and the assertions execute.
Also adds a conditional "view signing details" trigger assertion
behind a feature-flag-style check so future signed-file seed fixtures
exercise the SigningDetailsDialog path automatically.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>