Let \( S \) be the set of all values of \( \theta \in [-\pi, \pi] \) for which the system of linear equations
\( x + y + \sqrt{3}\,z = 0 \)
\( -x + (\tan \theta)\,y + \sqrt{7}\,z = 0 \)
\( x + y + (\tan \theta)\,z = 0 \)
has non-trivial solution. Then \( \dfrac{120}{\pi} \displaystyle\sum_{\theta \in S} \theta \) is equal to: