resolve_adapter matched sources by loose substring over the netloc, so a
look-alike host ('myyoutube.com', 'youtube.com.evil') misresolved. Match the
host exactly or as a subdomain via a _host_is() helper, and identify from the
netloc of BOTH source_ref and yt-dlp's webpage_url — the latter by host only,
never a substring over its path. This also restores a host signal to the
early-fill path (resolve_adapter(None, None, info)), which has no source_ref,
so a Facebook asset's uploader_url no longer depends on extractor_key being
present in the progress-hook info_dict.
Tests: look-alike hosts stay generic while real subdomains resolve; a
webpage_url netloc identifies the source when extractor_key is absent.