5.
已知倾斜角为\(\dfrac{π}{4} \)的直线经过抛物线\(r\):\({y}^{2}=2px\left(p > 0\right) \)的焦点\(F\),与抛物线\(r\)相交于\(A\)、\(B\)两点,且\(\left|AB\right|=8 \).
\((\)Ⅰ\()\)求抛物线的方程;
\((\)Ⅱ\()\)过点\(P\left(12,8\right) \)的两条直线\({l}_{1} \)、\({l}_{2} \)分别交抛物线\(r\)于点\(C\)、\(D\)和\(E\)、\(F\),线段\(CD\)和\(EF\)的中点分别为\(M\)、\(N.\)如果直线\({l}_{1} \)与\({l}_{2} \)的倾斜角互余,求证:直线\(MN\)经过一定点.