added support for simultan downloads in files and talk, support for background downloads, enhanced loading in files with retry

lib/widget/details_bottom_sheet.dart

@@ -4,12 +4,12 @@ import 'package:flutter/material.dart';
 /// custom event, etc.). All detail sheets in the app share this layout: drag
 /// handle on top, default theme background, optional ListTile-style header
 /// followed by a divider, scrollable body below.
-void showDetailsBottomSheet(
+Future<void> showDetailsBottomSheet(
   BuildContext context, {
   Widget? header,
   required List<Widget> Function(BuildContext sheetContext) children,
 }) {
-  showModalBottomSheet<void>(
+  return showModalBottomSheet<void>(
     context: context,
     isScrollControlled: true,
     showDragHandle: true,