PCIe Bracket Improvements

A few things that would be nice for the PCIe Bracket:

- [ ] Screw threads tapped into the extensions so you don't need to manually thread screws into bolts on the underside of the bracket (this is a bit finicky to do)
- [ ] USB and 12V power cutouts to match the actual ports used on the card (the PCIe bracket seems to press against those ports since the cutouts are sized to the individual plugs and not to the physical port hardware for the sockets

Start by locating the PCIe bracket model in the repository and inspect how its extensions and USB/12V cutouts are defined. Done means the extensions accept tapped screw threads and the cutouts clear the physical ports used on the card.

Written by the indexing model from the issue text.