Fix webui port binding: restore public access on 8081

The devops security pass incorrectly bound the webui to 127.0.0.1,
making it unreachable from the network. The webui is the user-facing
interface and must be publicly accessible. Internal-only services
(api :3000, radicale :5232, webdav :8080, rainloop :8888,
filegator :8082) retain their loopback bindings.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-compose.yml

@@ -223,7 +223,7 @@ services:
     build: ./webui
     container_name: cell-webui
     ports:
-      - "127.0.0.1:${WEBUI_PORT:-8081}:80"
+      - "${WEBUI_PORT:-8081}:80"
     restart: unless-stopped
     networks:
       cell-network: