Configure application to use a specific port and internal network

Updates Dockerfile and docker-compose.yml to expose port 4523 for the application and ensures it communicates with PostgreSQL over an internal Docker network.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: ae4037a0-2a6f-4530-9bac-79b543286bda
Replit-Commit-Checkpoint-Type: intermediate_checkpoint
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.env.example

@@ -9,9 +9,9 @@ PGHOST=postgres
 DATABASE_URL=postgresql://socialflow:changeme@postgres:5432/socialflow
 
 # Configuration de l'application
-PORT=5000
+PORT=4523
 NODE_ENV=production
-APP_URL=http://localhost:5000
+APP_URL=http://localhost:4523
 
 # Clé secrète pour les sessions (CHANGEZ CETTE VALEUR)
 SESSION_SECRET=your-secret-key-change-me-to-random-string