Let A, B, C be three points in the xy-plane, whose position vectors are given by \( \sqrt{3} \hat{i} + \hat{j} \), \( \hat{i} + \sqrt{3} \hat{j} \), and \( a\hat{i} + (1-a) \hat{j }\) respectively with respect to the origin \( O \). If the distance of the point C from the line bisecting the angle between the vectors \( \overrightarrow{OA} \) and \( \overrightarrow{OB} \) is \( \frac{9}{\sqrt{2}} \), then the sum of all possible values of \( a \) is: