usability fixes

lib/screens/history/history_controller.dart

@@ -1,4 +1,7 @@
 import 'package:flutter/material.dart';
+import 'package:intl/intl.dart';
+import 'package:url_launcher/url_launcher.dart';
+import 'package:qpay/config/app_config.dart';
 import 'package:qpay/http/http.dart';
 import 'package:qpay/models/api_response.dart';
 import 'package:qpay/models/pageable_model.dart';
@@ -183,6 +186,58 @@ class HistoryController extends ChangeNotifier {
     _safeNotify();
   }
 
+  /// Builds the fully-qualified download URL for the transactions report.
+  Uri _buildReportUrl({
+    required String workspaceId,
+    required DateTime startDate,
+    required DateTime endDate,
+  }) {
+    final df = DateFormat("yyyy-MM-dd'T'HH:mm:ss");
+    final start = Uri.encodeComponent(
+      df.format(
+        DateTime(startDate.year, startDate.month, startDate.day, 0, 0, 0),
+      ),
+    );
+    final end = Uri.encodeComponent(
+      df.format(
+        DateTime(endDate.year, endDate.month, endDate.day, 23, 59, 59),
+      ),
+    );
+    return Uri.parse(
+      '${AppConfig.baseUrl}/public/reports/transactions/download'
+      '?startDate=$start'
+      '&endDate=$end'
+      '&workspaceId=$workspaceId',
+    );
+  }
+
+  /// Opens the transactions report download URL in the device browser.
+  /// The browser handles the actual file download natively — no file I/O
+  /// or plugin channels required, works on Android, iOS, and web.
+  Future<void> downloadReport({
+    required String workspaceId,
+    required DateTime startDate,
+    required DateTime endDate,
+  }) async {
+    model.isActing = true;
+    _safeNotify();
+
+    try {
+      final uri = _buildReportUrl(
+        workspaceId: workspaceId,
+        startDate: startDate,
+        endDate: endDate,
+      );
+      await launchUrl(uri, mode: LaunchMode.externalApplication);
+    } catch (e) {
+      logger.e('Failed to open report URL: $e');
+      model.errorMessage = 'Failed to download report';
+    } finally {
+      model.isActing = false;
+      _safeNotify();
+    }
+  }
+
   void clearFilters() {
     model.statusFilter = null;
     model.typeFilter = null;
@@ -219,4 +274,4 @@ class HistoryController extends ChangeNotifier {
       },
     ];
   }
-}
+}