Multi-Tenant LMS Infrastructure with Secure Kubernetes Isolation

Design a Kubernetes-based multi-tenant learning management system architecture that guarantees complete tenant isolation using network policies, Pod Security Policies, and custom admission controllers. Create a detailed implementation plan that addresses potential security vulnerabilities, demonstrates namespace-level segregation, and implements granular RBAC controls for different institutional user roles. Include a comprehensive threat model explaining how each architectural component prevents cross-tenant data leakage and unauthorized access.