Beacon redirect-block test page

Test page that performs a first-party beacon request (to ./eviltracker-redirect), for which a 302 Redirect response is returned, redirecting the request to https://eviltracker.net/. It is expected that content blockers (e.g. the DuckDuckGo browsers / extension) will block the tracking request. This is an attempt to reproduce a reported macOS/iOS 26.5.2 WebKit tab-crash bug, see https://bugs.webkit.org/show_bug.cgi?id=318878 .