fix(desktop): add %u to Exec and complete tarball .desktop for URI handling

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

src-tauri/templates/app.desktop

@@ -3,7 +3,7 @@ Name={{name}}
 {{#if comment}}
 Comment={{comment}}
 {{/if}}
-Exec={{exec}}
+Exec={{exec}} %u
 Type=Application
 Icon={{icon}}
 Categories={{categories}}