A uniform solid disk of mass \(M\) and radius \(R\) is mounted on a fixed, frictionless axle passing through its center of mass. The disk is attached to a non-linear torsion spring that exerts a restoring torque \(\tau(\theta) = -\kappa \theta^3\), where \(\kappa\) is a positive constant and \(\theta\) is the angular displacement from equilibrium. The disk is released from rest at an initial angular displacement \(\theta = \theta_0 > 0\). Which of the following integral expressions correctly represents the angular speed \(\omega\) of the disk as it passes through the equilibrium position \(\theta = 0\)?