Make /opt/moonarch root-owned for multi-user support

Remove chown from archinstall custom-commands so the repo stays
root:root. Use sudo for git operations in update.sh. Any user with
sudo can now run moonarch-update without owning the repo.

README.md

@@ -63,7 +63,6 @@ Transform converts your system to Moonarch without reinstalling.
 ```bash
 # Clone the repo
 sudo git clone https://gitea.moonarch.de/nevaforget/moonarch.git /opt/moonarch
-sudo chown -R $(whoami):$(whoami) /opt/moonarch
 
 # Preview what will happen (no changes made)
 /opt/moonarch/scripts/transform.sh --dry-run