Make sure you are clear on your definitions. Blade angle (or pitch) is the angle between the plane of rotation and the chord line. Blade angle of attack is the angle between the relative airflow and the chord line.
For simplicity, let’s assume we’re executing a static takeoff with the brakes applied.
We’ve of course got our mixture and prop levers all the way forward.
We then smoothly advance the throttle, RPM and manifold pressure will increase accordingly.
As we then release the brakes, accelerate down the runway and introduce airspeed, the relative airflow changes (as you say it moves forward). The CSU then starts to proportionately increase the pitch and the blades move off their fine pitch stops and coarsen in order to maintain the same RPM (i.e. a constant speed).
So if the pitch has increased, by definition the blade angle has increased – all in order to avoid an overspeed condition and maintain the RPM that has been set.
And if the pitch has increased proportionally to the relative airflow, then the chord line has also changed proportionally to the relative airflow, thus there is no change to the angle of attack.