Give Hammerhead its own edge with a built-in dashboard route; setup.sh installs it with Blacktip instead of Caddy

HAMMERHEAD_SELF_DOMAIN creates an edge for this machine, writes its token to <data>/self-edge.env
and adds an https route for the dashboard to that edge's config, so no reverse proxy is needed.

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

agent.go

@@ -73,6 +73,9 @@ func (s *Server) edgeConfig(w http.ResponseWriter, r *http.Request) {
 			cfg.Mappings = append(cfg.Mappings, *m)
 		}
 	}
+	if m := s.selfMapping(e); m != nil {
+		cfg.Mappings = append(cfg.Mappings, *m)
+	}
 	cfg.MailEgress = []model.MailPolicy{}
 	for _, x := range s.st.MailEgress {
 		if x.EdgeID == e.ID && x.Enabled {