enrollment: actually emit enroll_uri from the admin endpoint

The previous commit's edit to the admin handler silently did not apply, so the
endpoint still returned just the token. Caught by deploying and looking at the
response rather than by trusting the build to have picked it up.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

server/cmd/echolot-server/main.go

@@ -234,7 +234,17 @@ func serve(cfg *config.Config) error {
 			http.Error(w, err.Error(), 500)
 			return
 		}
-		fmt.Fprintf(w, `{"token":%q,"expires_in_s":86400}`+"\n", tok)
+		// The whole bootstrap, not just the token: this is what gets pasted or turned into a
+		// QR code, and assembling it here is what keeps an operator from transcribing a pin by
+		// hand — a pin wrong by one character fails as an inscrutable TLS error days later.
+		w.Header().Set("Content-Type", "application/json")
+		enc := json.NewEncoder(w)
+		enc.SetEscapeHTML(false) // the link is full of / and =; escaping them helps nobody
+		_ = enc.Encode(map[string]any{
+			"token":        tok,
+			"expires_in_s": 86400,
+			"enroll_uri":   ctl.EnrollmentLink(tok),
+		})
 	})
 	adminSrv := &http.Server{Addr: cfg.AdminListen, Handler: admin, ReadHeaderTimeout: 10 * time.Second}
 	go func() { errCh <- fmt.Errorf("admin: %w", adminSrv.ListenAndServe()) }()