cmd and pageup issues

I noticed whilst trying to add the following two mappings that the pageup one didn't work

```
# dock and menu
ctrl + cmd + alt - pageup : skhd -k "ctrl - f2"
ctrl + cmd + alt - pagedown : skhd -k "ctrl - f3"
```
on investigation with `skhd --observe` I can see that if I press any modifier and page down the keycode goes to 0x79 (which is correct) but then with page up it only goes to 0x74 if the cmd key isn't pressed (so works with alt, shift, ctrl). The moment the cmd key is involved the detected keycode never changes from 0x37 to pageup. Holding the cmd key seems to block the detection of pageup.

Start by reproducing the mappings with skhd --observe, comparing pageup and pagedown while holding each modifier, especially cmd. Trace the keyboard-event handling entry point that converts these combinations to keycodes. Done means cmd+pageup reports the correct keycode and the mapping invokes ctrl-f2, without regressing the other modifier combinations.

Written by the indexing model from the issue text.