#981 jumper standalone: 7 of 40 client tests fail against jumper's own migrations (task status columns shifted)

EARS: When the jumper repository's migrations are applied to an empty PostgreSQL 16 or 18 database, the jumper client test suite shall pass. Found by the #918 jumper pipeline (emulated in ci-python:3.13; services postgres:16 and, earlier, PostgreSQL 18.6; jumper 695c8ad plus the CI conftest change that reads JUMPER_TEST_DSN). 33 pass, 7 fail: TestCompleteRun::test_complete_run, TestFailAndRetry::test_fail_with_retry, ::test_fail_permanent_max_attempts_reached, ::test_force_permanent_failure, TestCancelTask::test_cancel_task, TestTenantId::test_tenant_id_propagates_on_retry, TestTaskAndRunStatus::test_get_task_status. Symptom: get_task_status returns state=None or a datetime in the state field (assert datetime(...) == 'failed'), so the row the client unpacks does not match the columns jumper's migrations create. Highway itself deploys jumper's schema through the engine migrations, so this is a gap between jumper's standalone migrations and its client, not necessarily a production fault. Before #918 the suite could only run through 'docker compose up' on localhost:5433.