update account admin luôn tồn tại

.env.example

@@ -18,6 +18,11 @@ ACCESS_TOKEN_EXPIRE_MINUTES=60
 # Port exposed on the host for the Next.js frontend
 FRONTEND_PORT=3011
 
+# ── Default admin account (created automatically on first start) ─────────────
+ADMIN_USERNAME=admin
+ADMIN_PASSWORD=Admin@12345
+ADMIN_EMAIL=admin@lms.local
+
 # ── Docker Hub images (optional — leave blank to build locally) ───────────────
 # Set these on the target machine so docker compose pull works without building
 # BACKEND_IMAGE=your_dockerhub_username/lms-backend:latest