Mention OS with subject of logs sent when app is stuck on lockscreen …

…for more than 15 seconds. This will let us identify OS when logs are not attached

mobile/lib/main.dart

@@ -186,7 +186,7 @@ Future<void> _init(bool isBackground, {String via = ''}) async {
       if (!initComplete && !isBackground) {
         sendLogsForInit(
           "[email protected]",
-          "Stuck on splash screen for >= 15 seconds",
+          "Stuck on splash screen for >= 15 seconds on ${Platform.operatingSystem}",
           null,
         );
       }