chore(packaging): add qobuzapp scheme to desktop files

All 6 .desktop files now declare x-scheme-handler/qobuzapp in their
MimeType line, enabling OS-level link capture for qobuzapp:// URLs.

src-tauri/templates/app.desktop

@@ -11,4 +11,4 @@ Terminal=false
 StartupWMClass=com.blitzfc.qbz
 StartupNotify=true
 Keywords=music;audio;qobuz;hifi;streaming;audiophile;flac;
-MimeType=x-scheme-handler/qbz;
+MimeType=x-scheme-handler/qbz;x-scheme-handler/qobuzapp;