If \( f \) is continuous at \( x=\dfrac{\pi}{2} \), then the value of \( \displaystyle \int\limits_{0}^{3b-6} \left|x^2+2x-3\right|\,dx \) is:
\( 5 \)
\( 2 \)
\( 3 \)
\( 4 \)