feat(dev-db): PG_* parametrizado p/ banco dev isolado via .env (default=produção)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docker-compose.yml

@@ -10,20 +10,20 @@ services:
       - subdominio-net
 
   backend:
-    image: node:20-alpine
+    build: ./backend
     container_name: subdominio-backend
     restart: unless-stopped
     working_dir: /app
-    command: node server.js
     environment:
-      - PG_HOST=10.99.0.3
+      - PG_HOST=${SUB_DB_HOST:-10.99.0.3}
       - PG_PORT=5432
-      - PG_DATABASE=subdominio
-      - PG_USER=mercado_admin
-      - PG_PASSWORD=mErC4d0_2026_Club3!#
+      - PG_DATABASE=${SUB_DB_NAME:-subdominio}
+      - PG_USER=${SUB_DB_USER:-mercado_admin}
+      - PG_PASSWORD=${SUB_DB_PASS:-mErC4d0_2026_Club3!#}
       - PORT=8019
     volumes:
       - ./backend:/app
+      - /app/node_modules
     networks:
       - subdominio-net
       - soc