In modern enterprise networks, complicated rule-based signatures, fragmented alerts, encrypted traffic, and analyst workloads are delaying the ability to recognize and contain incidents, as the need grows for faster correlation of heterogeneous telemetry. This study evaluates an LLM-augmented network-forensics architecture for threat detection, evidence interpretation, and controlled automated response, while retaining deterministic security controls. The 30-day controlled digital-twin experiment in the medium-sized hybrid enterprise resulted in about 18.6 million security events. The events were correlated into 1,200 incident windows: 480 malicious and 720 benign. Precision, F1-score, Recall, FPR, ROC-AUC, investigation latency, and response accuracy were used to compare the proposed hybrid system with XGBoost, SIEM Rules, and a transformer-based anomaly detection architecture. In the controlled digital-twin evaluation, the LLM-augmented hybrid system achieved an F1 score of 94.2%, a false-positive rate of 3.1%, a mean detection time of 2.6 minutes, a mean response time of 13.4 minutes, and a response-recommendation accuracy of 92.1%. Through retrieval-augmented generation, either with or without schema validation, the amount of unsupported claims decreased from 14.6% to 3.8%. Results showed that LLM performance as contextual reasoning, explanation, and orchestration components in guarded workflows was most effective. For high-impact actions impacting critical assets, privileged identities, or production systems, human approval was required. Multi-enterprise validation, adversarial testing, and privacy-preserving model adaptation should be addressed in the future.