Given two planes with equations \( \mathbf{r} \cdot (\mathbf{i} - \mathbf{j} + \mathbf{k}) = 5 \) and \( \mathbf{r} \cdot (2\mathbf{i} + \mathbf{j} - \mathbf{k}) = 3 \). A plane \( \pi \) passing through the line of intersection of these two planes also passes through the point (0,1,2). If the equation of \( \pi \) is \( \mathbf{r} \cdot (a\mathbf{i} + b\mathbf{j} + c\mathbf{k}) = m \), determine the value of \( \frac{bc}{a^2} \):