fix: sync multi-day work hours accounting

Aggregate task work-hour rows into travel-cost calculations and monthly servicer reporting, and keep the frontend calendar aligned with the task work-hours source.

backend/modules/task_management/serializers.py

@@ -91,6 +91,7 @@ class TaskSerializer(serializers.ModelSerializer):
     vehicle_owner_name = serializers.SerializerMethodField()
     vehicle_asset_type = serializers.SerializerMethodField()
     crane_serial_number = serializers.SerializerMethodField()
+    work_hours_table = serializers.SerializerMethodField()
     template_id = serializers.UUIDField(write_only=True, required=False, allow_null=True)
     auto_close_work_order = serializers.BooleanField(write_only=True, required=False)
 
@@ -100,7 +101,7 @@ class TaskSerializer(serializers.ModelSerializer):
             'id', 'title', 'description', 'status',
             'assigned_to', 'assigned_to_name',
             'vehicle', 'vehicle_registration', 'vehicle_make', 'vehicle_model',
-            'vehicle_owner_name', 'vehicle_asset_type', 'crane_serial_number',
+            'vehicle_owner_name', 'vehicle_asset_type', 'crane_serial_number', 'work_hours_table',
             'work_order', 'work_order_label',
             'scheduled_date',
             'service_report_note',
@@ -212,3 +213,9 @@ class TaskSerializer(serializers.ModelSerializer):
         if not obj.vehicle_id:
             return None
         return obj.vehicle.crane_serial_number or None
+
+    def get_work_hours_table(self, obj):
+        table = getattr(obj, 'work_hours_table', None)
+        if not table:
+            return None
+        return TaskWorkHoursTableSerializer(table).data