Fix desktop shortcut on localized systems

Installing the station desktop launcher on a non-English system put the shortcut in the wrong place, so it never appeared for the operator.

• Fixed the launcher to use the system's localized Desktop folder (such as Bureau on French installs) instead of always creating an English "Desktop" folder.
• Aligned shortcut install, detection, and removal across Linux, Windows, and macOS so they all target the same folder, including OneDrive-redirected desktops on Windows.