Front wheel "shudder" or "pulse" when braking
By your description, it totally seems to be some slight irregularity on rim surface, be it a bent spot, some fluctuation around valve-hole or seam, or some slight variation on total width.

I had the exact problem you described three times: after hitting a pothole too hard once, and after my bike fell off a moving car's bike rack thereafter.

Both times, it was some rim irregularity, and it was on the same rim. First time, I kept riding and the very rim wearing out with braking eventually solved the problem. Second time, I had to put a new rim, because the "pulse" was very intense and dangerous (fork flexing and all).

The third time I had this problem, I had a defective rim which eventually cracked on the side, and I felt a progressive worsening of this "pulse".

AND HERE GOES THE SOLUTION!

I noticed this irregularity caused an assymmetric MONLIGHT REFLECTION because I was riding at night, leaned the bike to the side, and was marevelled by the beautiful circle of moonlight on the shiny breaking surface of the rim. But there was a bent spot, pretty much invisible to direct observation.

So, I propose you go with your bike close to a shadowed wall on a very sunny day, and use the braking surface of the rim to reflect sunlight on this shadowed wall, optionally letting the wheel turn slowly, and repeating the procedure with the other side of the rim.

For sure, if there is a bent spot, the slightest one, you will see it.

You can increase the distance to the wall to make the effect more obvious, and you should expect some natural assymmetry. The "abnormal" thing to watch would be a very localized spot of aberrant light distrtibution.

EDIT: suppose you found the micro-bent spot, a good way to wear it away is to put not-so-expensive brake pads, go to your favourite muddy downhill track in a wet day (preferrably one where the weels completely sink in the mud), and use the brakes mercyless. Your rim will begin to shine!! (pun intended ;o)

Hope it helps!

(well, you could always turn the bike upside down, spin the wheel, close your eyes, and literally feel variations on rim surface with your bare fingers. It is not so sensitive as the sunlight method. Do it with caution!)