Let the line \( y - x = 1 \) intersect the ellipse \( \frac{x^{2}}{2} + \frac{y^{2}}{1} = 1 \) at the points \( A \) and \( B \). Then the angle made by the line segment \( AB \) at the center of the ellipse is:
\( \frac{\pi}{2} + 2\tan^{-1}\!\left(\frac{1}{4}\right) \)
\( \frac{\pi}{2} + \tan^{-1}\!\left(\frac{1}{4}\right) \)
\( \frac{\pi}{2} - \tan^{-1}\!\left(\frac{1}{4}\right) \)
\( \pi - \tan^{-1}\!\left(\frac{1}{4}\right) \)