An uncharged, thin spherical shell of radius \(R\) is assembled by an external agent that brings infinitesimal charge elements from infinity and deposits them uniformly onto the shell until a final net charge \(Q\) is reached. The work required to assemble the shell equals the total electrostatic potential energy \(U\) stored in the resulting electric field. This stored energy can be determined by integrating the electric field energy density, \(u_E = \dfrac{1}{2}\varepsilon_0 E^2\), over all space, where \(E\) is the electric field magnitude at a distance \(r\) from the center of the shell. Which of the following integral expressions correctly represents \(U\)?