Simple solution:

If you enable it, KStars shows the Alt/Az in the status bar. Hitting
'N' and hovering over the north pole, I see the azimuth is 0 degrees.
Hitting 'E' and hovering over the eastern horizon, I see that the
azimuth is about 90 degrees.

So we follow N = 0, E = 90 convention.

Regards
Akarsh