Express 5 (path-to-regexp v8+) dropped support for the *paramName
wildcard syntax from Express 4. The route registered as
'/api/auth/*authPath' silently fails to match any sub-path, causing
every /api/auth/* request to return 404 instead of reaching the
better-auth handler.
Fixes: #2898
Change the route to '/api/auth/{*authPath}', the correct named
catch-all syntax in Express 5.
