Front wheel shifting left on braking with new front shock and fender install
First thing to do is check if the wheel is actually moving in the fork, or that the fork has slop or play in it.

Stand next to the bike, hold the bars, apply front brake and try to move the bars side-side and front-back. If you feel slop or play, don't ride it and take the bike straight back to the store that did the installation and have them fix it.

It may be that braking is causing the fork to bend slightly and move the wheel left. You could also take the bike to the store, show them the problem  and ask them to check their work.