If $[x]$ is the greatest integer $\le x$, then $\pi^2 \int_{0}^{2} \left(\sin \frac{\pi x}{2}\right) (x - [x])^{[x]} dx$ is equal to:
\( 2(\pi + 1) \)
\( 2(\pi - 1) \)
\( 4(\pi + 1) \)
\( 4(\pi - 1) \)