Withhold a site name that could be the recipe link's host

A page that names no site is stored under its host, which may be the
pasted link's (a token in a subdomain) or a redirect's. The dinner
detail now returns source.site_name only when the stored name could not
be a host: the link's own host, an IP address or a dotted host name is
withheld as null, so "Recipe from {site}" shows only real attribution.
The extractor's host fallback is shared as recipes.HostSiteName.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/dinners/export_test.go

@@ -71,3 +71,6 @@ func (s *Service) RunGroundJob(ctx context.Context, p GroundJob) (string, error)
 	r, err := s.runGroundJob(ctx, p, nil)
 	return r.GroundingStatus, err
 }
+
+// PageSiteName is pageSiteName.
+var PageSiteName = pageSiteName