Well, I can't explain this, but here's what ended up happening:

After struggling for a long time, I decided, against my beter judgment, to see if the motor would drive the window up, knowing there was a risk of burning up the motor if I tried turning it very long against a jammed window. So I held my breath, grabbed the bottom of the window with one hand, and quickly flicked the switch with the other. Lo and behold, the window moved up. In fact, I can raise it almost all the way to the top with the motor.

The reason the motor can now move the window is that while struggling to get the window free, the clip that holds the regulator to the window at the rear popped out of the window. In fact, what looks like the part of the regulator that connects the cable to the clip fell to the bottom of the door frame, so the regulator is definitely toast (I ordered a new one from autohausaz). So, somehow the regulator must have been jammed up in the rear, and once it came loose of the window, the motor can now drive the window up. I still don't understand why I can't move it manually - I don't know anything about how power windows work - I guess the window can't be moved by hand as long as the regulator is connected to the motor.

Once I get the new regulator, I'll hopefully be able to figure out how the whole contraption works, and will hopefully be able to do a post mortem on what happened, so the whole job will be a lot easier the next time one breaks. Also, by comparing the old one to the new one, I'll be able to see exactly where the old one broke, and I'll see if it's possible to reinforce the weak spot, like you can on an E46.

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2003 X5 4.4i
1992 Porsche 968
2007 328i
2014 Subaru Forester XT