Let \( S=\{\theta \in (-2\pi,2\pi): \cos\theta+1=\sqrt{3}\sin\theta\} \). Then \( \sum_{\theta\in S}\theta \) is equal to:
\(- \frac{2\pi}{3} \)
\( -\frac{4\pi}{3} \)
\( \frac{2\pi}{3} \)
\( \frac{4\pi}{3} \)