Obtain the value of \( \Delta = \begin{vmatrix} 1+x & 1 & 1 \\ 1 & 1+y & 1 \\ 1 & 1 & 1+z \end{vmatrix} \) in terms of \( x, y \) and \( z \). Further, if \( \Delta = 0 \) and \( x, y, z \) are non-zero real numbers, prove that \( x^{-1} + y^{-1} + z^{-1} = -1 \).