Mean-Field Game Equilibrium for SEIR Epidemics on Networks // Implements the forward-backward sweep algorithm for computing Nash equilibrium contact policies in SEIR epidemic mean-field games on heterogeneous contact networks, as described in Wang (2026) doi:10.5281/zenodo.19381052. Supports both heterogeneous networks with arbitrary degree distributions (e.g., truncated Poisson) and homogeneous networks. Computes equilibrium susceptible contact effort, value functions, epidemic trajectories, and the effective reproduction number Rt.