feat: migrate application port from 3000 to 4001 and fix circular dependencies

- Change default port to 4001 across all configuration files (server.js, docker-compose.yml, .env, Dockerfile)
- Update frontend API URL to use new port 4001
- Fix circular dependency issues in route files by using process.env.SERVER_DIR instead of importing from server.js
- Apply to all routes: auth.js, backup.js, logs.js, players.js, rcon.js, server.js, whitelist.js
- Fix environment variable loading in start.sh to properly handle paths with spaces
- Quote SERVER_DIR path in .env to preserve spaces in directory paths
- Update all documentation references from port 3000 to 4001 (README, QUICKSTART, CONFIGURATION, INDEX)
- Remove debug console.log statements from auth.js
- Remove test utility file test-ops.js

Fixes: Port conflict issues, circular dependency warnings, environment variable parsing

install.sh

@@ -33,7 +33,7 @@ echo ""
 echo "📝 Prochaines étapes:"
 echo "1. Modifiez backend/.env avec la bonne configuration"
 echo "2. Lancez le serveur: cd backend && npm start"
-echo "3. Accédez à l'interface: http://localhost:3000"
+echo "3. Accédez à l'interface: http://localhost:4001"
 echo ""
 echo "ℹ️  IMPORTANT: Activez RCON dans le server.properties du serveur MC:"
 echo "   - enable-rcon=true"