feat: redirects screen

- golem15.seo.redirects list and form (UI-SPEC C8): chain rows marked,
  status, match, origin and chain filters, the navigation item lands here
- a field-less extension on the controller refuses a loop with
  redirects.loop on target, answers the chain notice and records history
- the status dropdown posts text, read through RedirectStatus

classes/resolver.go

@@ -582,7 +582,7 @@ func (r *Resolver) redirectAnswer(self string, ch Chain) Result {
 		logRedirectCycle(self, ch)
 		res.Action, res.Status = ActionNotFound, 404
 	case ch.Gone:
-		res.Action, res.Status = ActionGone, models.Status410
+		res.Action, res.Status = ActionGone, int(models.Status410)
 	default:
 		res.Action, res.Status, res.Location = ActionRedirect, ch.Status, AbsoluteURL(r.Service.SiteURL(), ch.Final)
 	}