feat(worker): adopt canonical public URL

packaging/systemd/worker.env.example

@@ -2,7 +2,9 @@ RSMON_URL=https://rsmon.ru
 RSMON_TOKEN=replace-with-worker-token
 WORKER_HOST=127.0.0.1
 WORKER_PORT=27401
-WORKER_URL=
+# Advertised public origin: absolute http(s) origin (scheme + host, no path).
+# PUBLIC_URL is canonical; WORKER_URL is a bounded-migration legacy alias.
+PUBLIC_URL=
 WORKER_LOGIN=admin
 WORKER_PASSWORD=replace-with-a-long-random-password
 RSMON_WEBAPP_DATA_DIR=/var/lib/rsmon-worker/webapp