chore(infra): run backend container with dynamic volume mounting

docker-compose.yml

@@ -10,10 +10,11 @@ services:
       - subdominio-net
 
   backend:
-    build:
+    image: node:20-alpine
-      context: ./backend
     container_name: subdominio-backend
     restart: unless-stopped
+    working_dir: /app
+    command: node server.js
     environment:
       - PG_HOST=10.99.0.3
       - PG_PORT=5432
@@ -22,7 +23,7 @@ services:
       - PG_PASSWORD=mErC4d0_2026_Club3!#
       - PORT=8019
     volumes:
-      - ./backend/config.json:/app/config.json
+      - ./backend:/app
     networks:
       - subdominio-net
       - soc