A torsional pendulum consists of a uniform solid disk of mass \(M\) and radius \(R\) suspended in a horizontal plane by a thin vertical wire attached to its center. When the disk is rotated through an angular displacement \(\theta\) from equilibrium, the wire exerts a restoring torque \(\tau = -\kappa\theta\), where \(\kappa\) is a positive constant. The disk is released from rest from an initial angular displacement \(\theta_0\). What is the period of rotational oscillation of the disk?