如图，四棱锥\(P-\text{ABCD}\)的底面是矩形，\(\text{PD}\text{⊥}\)底面\(\text{ABCD}\text{,}M\)为\(\text{BC}\)的中点，且\(\text{PB}\text{⊥}\text{AM}\text{.}\)

\((1)\)证明：平面\(\text{PAM}\text{⊥}\)平面\(\text{PBD}\)；

\((2)\)若\(\text{PD}\text{=}\text{DC}\text{=}1\)，求四棱锥\(P-\text{ABCD}\)的体积．