设数列 $\left\{x_n\right\}$ 满足: $x_1=2, x_{n+1}=\frac{x_n^2}{1-x_n+x_n^2}(n=1,2, \cdots)$
(1) 证明: $\lim _{n \rightarrow \infty} x_n$ 存在, 并求其值;
(2) 求 $\lim _{n \rightarrow \infty}\left[\left(\frac{1}{x_1}-1\right)^2+\left(\frac{1}{x_2}-1\right)^2+\cdots+\left(\frac{1}{x_n}-1\right)^2\right]$.