已知数列\( \left\{{a}_{n}\right\}​\)为等差数列\( ,​\)且\( {a}_{3}=-6,{a}_{6}=0​\)
(1)求数列\( \left\{{a}_{n}\right\}​\)的通项公式;
(2)若等比数列\( \left\{{a}_{n}\right\}​\)满足\( {b}_{1}=-8,{b}_{2}={a}_{1}+{a}_{2}+{a}_{3},\mathrm{求}\left\{{b}_{n}\right\}​\)的前n项和.