fix(ui): fix various UI issues (#1518)

ui/flutter/lib/features/settings/presentation/widgets/download_categories_setting.dart

@@ -7,6 +7,7 @@ import '../../../../core/utils/breakpoints.dart';
 import '../../../../shared/theme/app_design_tokens.dart';
 import '../../../../shared/theme/app_palette.dart';
 import '../../../../shared/widgets/app_path_picker_field.dart';
+import '../../../../shared/widgets/app_path_placeholder_button.dart';
 import '../../../../shared/widgets/app_primary_button.dart';
 import '../../../../shared/widgets/app_text_field.dart';
 import '../../../../l10n/l10n.dart';
@@ -180,6 +181,14 @@ Future<DownloadCategoryDraft?> showDownloadCategoryDialog(
                   desktopWidth: AppDesignTokens.settingsFormControlWidth,
                   allowAndroidEditing: true,
                 ),
+                const SizedBox(height: AppDesignTokens.space4),
+                Align(
+                  alignment: AlignmentDirectional.centerStart,
+                  child: AppPathPlaceholderButton(
+                    key: const ValueKey('download-category-placeholders'),
+                    controller: pathController,
+                  ),
+                ),
                 if (validationMessage != null) ...[
                   const SizedBox(height: 8),
                   Text(validationMessage!, style: TextStyle(color: palette.error, fontSize: 12)),