The /ugc page's routes and the UGC links' icon and mesh routes each had
their own copy of the curl request and its short cache. Both use
UgcFetch now: the URL is worked out on the web thread, the request and
cache run on worker threads. Players' errors still don't name the
internal URL.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
