vpn: aggregate all import errors

- we are dumb about importing by just trying to import everythting
- that caused errors to not be represented correctly
- just aggregate them all and present them in toast details
- Better would be to detect the type of file being imported, but this is
  better than nothing

quickshell/Services/VPNService.qml

@@ -95,7 +95,7 @@ Singleton {
             }
 
             importError = response.result.error || "Import failed";
-            ToastService.showError(importError);
+            ToastService.showError(I18n.tr("Failed to import VPN"), importError);
         });
     }