Configure the system to connect using the Nginx reverse proxy network

Updates the Docker configuration to use the `nginx_default` network and removes the custom `regisflow_network`.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 91318273-c764-4fd4-be04-bdc12c38af32
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/0715008c-7244-40f4-befc-26c014852236/2c8fdf94-4b36-4c45-81d5-036b422d1515.jpg

docker-compose.yml

@@ -7,8 +7,6 @@ services:
   regisflow-db:
     image: postgres:15-alpine
     container_name: regisflow-db
-    networks:
-      - regisflow_network
     environment:
       POSTGRES_DB: regisflow
       POSTGRES_USER: regisflow
@@ -31,8 +29,6 @@ services:
       context: .
       target: production
     container_name: regisflow-app
-    networks:
-      - regisflow_network
     depends_on:
       regisflow-db:
         condition: service_healthy
@@ -65,8 +61,8 @@ volumes:
   backup_data:
   logs_data:
 
-# Réseau dédié RegisFlow pour isolation et facilité de gestion
+# Utilisation du réseau nginx_default existant
 networks:
-  regisflow_network:
-    driver: ${NETWORK_DRIVER:-bridge}
-    name: regisflow_network
+  default:
+    external: true
+    name: nginx_default