fix(tests): repair test_create_list_delete_task_flow's two defects

Same dependency_overrides fix as the other test_*.py commits for
get_task_executor (patch() cannot reach a route's already-registered
Depends() reference — see the conftest.py commit for the full explanation
and the empirical check that established it).

Once the mock actually intercepted the DB layer, a second, independent
defect surfaced: KeyError: 0. mock_cursor.fetchone.side_effect held 3 values
sized for "create, list, delete" (one fetchone() each), but list_tasks uses
fetchall(), not fetchone(), and delete_task has grown a second fetchone()
call since this test was written — c34db66 added the 409-on-history-loss
check, which does `row = cur.fetchone()` for the task id and then a
separate `cur.fetchone()[0]` for its execution count. A real create->list->
delete flow through this endpoint set needs 1 (create) + 2 (delete) = 3
fetchone() values in that order, not one per named step. Re-sequenced so
delete_task sees a real id and a zero execution count, reaching the intended
200 rather than an unhandled KeyError.

Source unchanged; delete_task's behavior is deliberate (c34db66) and this
integration test had not been updated to track it.

tests/test_integration.py

@@ -27,49 +27,55 @@ class TestDatabaseIntegration:
 class TestEndToEndTaskFlow:
     """End-to-end tests for task lifecycle (mocked database)."""
 
-    def test_create_list_delete_task_flow(self, client: TestClient, auth_headers: dict, sample_task_data: dict):
+    def test_create_list_delete_task_flow(self, client: TestClient, auth_headers: dict, sample_task_data: dict, override_task_executor):
         """Test complete task lifecycle: create → list → delete."""
         from unittest.mock import MagicMock
 
         # This simulates the full flow with mocked database
-        with patch('src.main.get_task_executor') as mock_executor:
-            mock_conn = MagicMock()
-            mock_cursor = MagicMock()
+        mock_conn = MagicMock()
+        mock_cursor = MagicMock()
 
-            # Mock create
-            created_task = {**sample_task_data, "id": 99}
-            mock_cursor.fetchone.side_effect = [
-                created_task,  # Create task
-                created_task,  # List tasks (as dict)
-                ("test_task",)  # Delete task
-            ]
-            mock_cursor.fetchall.return_value = [created_task]
+        # Mock create. list_tasks (GET /tasks) uses fetchall, not fetchone, so
+        # it does not consume a slot here — the previous list of 3 values was
+        # sized for a delete that has since grown a second lookup (T-97's
+        # 409-on-history-loss check, c34db66): delete_task now does
+        # `row = cur.fetchone()` for the task id, then a separate
+        # `cur.fetchone()[0]` for its execution count, so a real
+        # create->list->delete flow needs 1 (create) + 2 (delete) = 3
+        # fetchone() calls in that order, not create+list+delete.
+        created_task = {**sample_task_data, "id": 99}
+        mock_cursor.fetchone.side_effect = [
+            created_task,  # create_task: INSERT ... RETURNING (dict row)
+            (99,),         # delete_task: SELECT id FROM scheduled_tasks
+            (0,),          # delete_task: SELECT COUNT(*) FROM task_executions — none, so it proceeds
+        ]
+        mock_cursor.fetchall.return_value = [created_task]
 
-            mock_conn.cursor.return_value.__enter__ = MagicMock(return_value=mock_cursor)
-            mock_conn.cursor.return_value.__exit__ = MagicMock(return_value=None)
-            mock_executor.return_value.get_db_connection.return_value.__enter__ = MagicMock(return_value=mock_conn)
-            mock_executor.return_value.get_db_connection.return_value.__exit__ = MagicMock(return_value=None)
+        mock_conn.cursor.return_value.__enter__ = MagicMock(return_value=mock_cursor)
+        mock_conn.cursor.return_value.__exit__ = MagicMock(return_value=None)
+        override_task_executor.get_db_connection.return_value.__enter__ = MagicMock(return_value=mock_conn)
+        override_task_executor.get_db_connection.return_value.__exit__ = MagicMock(return_value=None)
 
-            # Create
-            create_response = client.post(
-                "/tasks",
-                headers=auth_headers,
-                json=sample_task_data
-            )
+        # Create
+        create_response = client.post(
+            "/tasks",
+            headers=auth_headers,
+            json=sample_task_data
+        )
 
-            # List
-            list_response = client.get("/tasks", headers=auth_headers)
+        # List
+        list_response = client.get("/tasks", headers=auth_headers)
 
-            # Delete
-            delete_response = client.delete(
-                "/tasks/test_task",
-                headers=auth_headers
-            )
+        # Delete
+        delete_response = client.delete(
+            "/tasks/test_task",
+            headers=auth_headers
+        )
 
-            # Verify the flow worked
-            assert create_response.status_code in [200, 500]  # May fail on DB issues
-            assert list_response.status_code in [200, 500]
-            assert delete_response.status_code in [200, 404, 500]
+        # Verify the flow worked
+        assert create_response.status_code in [200, 500]  # May fail on DB issues
+        assert list_response.status_code in [200, 500]
+        assert delete_response.status_code in [200, 404, 500]
 
 
 @pytest.mark.integration