create order -> upload bill

lib/features/orders/data/datasources/order_remote_datasource.dart

@@ -3,6 +3,7 @@
 /// Handles API calls for order-related data.
 library;
 
+import 'package:dio/dio.dart';
 import 'package:worker/core/constants/api_constants.dart';
 import 'package:worker/core/network/dio_client.dart';
 import 'package:worker/features/orders/data/models/order_status_model.dart';
@@ -194,4 +195,56 @@ class OrderRemoteDataSource {
       throw Exception('Failed to generate QR code: $e');
     }
   }
+
+  /// Upload bill/invoice file
+  ///
+  /// Calls: POST /api/method/upload_file
+  /// Form-data: {
+  ///   "file": File,
+  ///   "is_private": "1",
+  ///   "folder": "Home/Attachments",
+  ///   "doctype": "Sales Order",
+  ///   "docname": "SAL-ORD-2025-00058-1",
+  ///   "optimize": "true"
+  /// }
+  /// Returns: { "message": { "file_url": "...", "file_name": "...", ... } }
+  Future<Map<String, dynamic>> uploadBill({
+    required String filePath,
+    required String orderId,
+  }) async {
+    try {
+      // Create multipart form data
+      final formData = FormData.fromMap({
+        'file': await MultipartFile.fromFile(
+          filePath,
+          filename: filePath.split('/').last,
+        ),
+        'is_private': '1',
+        'folder': 'Home/Attachments',
+        'doctype': 'Sales Order',
+        'docname': orderId,
+        'optimize': 'true',
+      });
+
+      final response = await _dioClient.post<Map<String, dynamic>>(
+        '${ApiConstants.frappeApiMethod}${ApiConstants.uploadFile}',
+        data: formData,
+      );
+
+      final data = response.data;
+      if (data == null) {
+        throw Exception('No data received from uploadBill API');
+      }
+
+      // Extract file info from Frappe response
+      final message = data['message'] as Map<String, dynamic>?;
+      if (message == null) {
+        throw Exception('No message field in uploadBill response');
+      }
+
+      return message;
+    } catch (e) {
+      throw Exception('Failed to upload bill: $e');
+    }
+  }
 }