Legacy Smart City frameworks (2015–2024) primarily functioned as centralized data-harvesting pipelines characterized by high latency and static logic. This paper proposes Neural Urbanism, a paradigm where the built environment operates as a Distributed Cognitive Entity (DCE). We introduce the SAGE (Self-Actualizing Autonomous Global Ecosystem) architecture, which replaces centralized cloud control with Agentic Infrastructure powered by AI-RAN and distributed User Plane Function (dUPF). By modeling the city as a mesh of autonomous agents capable of local inference and peer-to-peer resource negotiation, we demonstrate a system that achieves sub-1ms latency and inherent structural resilience without a single point of failure.