This paper proposes a novel framework for Smart Spectrum Intelligence (SSI) using AI-guided quantum sensing in Terahertz (THz)-enabled broadband networks. As data-hungry applications outpace traditional spectrum utilization models, the THz band offers ultra-wide bandwidth for beyond-5G and 6G systems. However, the volatility, molecular absorption, and sensitivity challenges of THz propagation demand adaptive and intelligent spectrum sensing mechanisms. We integrate reinforcement learning-based dynamic spectrum access (DSA), quantum entanglement-assisted channel prediction, and noise-resilient quantum sensors to enable reliable, real-time spectrum characterization and allocation. Our architecture introduces a hybrid AI–quantum layer with terahertz-adapted KPIs, and we evaluate it via simulation and modeling benchmarks. This work addresses unsolved challenges in spectrum scarcity, sub-optimal allocation, and sensing latency, proposing a shift toward trust-aware, intelligent, and quantum-enhanced spectral ecosystems.