cachy-update tweak should be enabled via XDG autostart

In https://github.com/Antiz96/arch-update/issues/599, we see that when using KDE Plasma, there can be a race condition on log out, such that the service is stopped too late, resulting in repeated crashes of arch-update-tray. The workaround is to use XDG autostart to start arch-update-tray on login: https://github.com/Antiz96/arch-update/issues/599#issuecomment-4773497841.

CachyOS Hello should be tweaked, such that it uses XDG autostart to enable arch-update-tray, instead of the user service.

Start by locating how CachyOS Hello currently enables arch-update-tray's user service, then review the linked arch-update issue and its XDG autostart workaround. Done means the tweak enables arch-update-tray through XDG autostart instead of the user service, with the login behavior verified in KDE Plasma.

Written by the indexing model from the issue text.