docs(backend): add .env.example

backend/.env.example

@@ -0,0 +1,16 @@
+# Server
+NODE_ENV=development
+PORT=4001
+
+# Database (MySQL)
+DB_HOST=localhost
+DB_PORT=3306
+DB_USER=originsdigital
+DB_PASSWORD=
+DB_NAME=originsdigital
+
+# SuperOAuth — service d'authentification externe
+SUPER_OAUTH_URL=https://superoauth.tetardtek.com
+
+# CORS — URL du frontend autorisé
+FRONTEND_URL=http://localhost:5173