The Tauri .desktop template was missing %u in the Exec line, preventing
the desktop environment from passing qobuzapp:// URIs as arguments when
launched from the browser. The tarball .desktop was also missing MimeType,
StartupWMClass, and StartupNotify fields.
Closes#44
cc
Set GTK_APPLICATION_ID for proper WM_CLASS and add desktop template
with StartupWMClass for correct process identification on Linux.
Also add window label for Tauri window configuration.