fix(lint): resolve ruff errors in tests and run_tests.py

- Fix import sorting (I001)
- Remove unused imports and variables (F401, F841)
- Add noqa for test code (S106 hardcoded passwords, S314 XML parsing)
- Auto-format with ruff format

tests/apps/core/test_background_jobs.py

@@ -187,7 +187,7 @@ class BackgroundJobServiceTest(TestCase):
     def test_get_user_jobs_with_status_filter(self):
         """Тест фильтрации по статусу."""
         user_id = 456
-        job1 = BackgroundJobService.create_job(
+        BackgroundJobService.create_job(
             task_id="task-pending",
             task_name="test.task",
             user_id=user_id,
@@ -212,7 +212,7 @@ class BackgroundJobServiceTest(TestCase):
     def test_get_active_jobs(self):
         """Тест получения активных задач."""
         # Создаём задачи с разными статусами
-        job_pending = BackgroundJobService.create_job(
+        BackgroundJobService.create_job(
             task_id="job-active-pending",
             task_name="test.task",
         )