Make lint-backend green, and regenerate the stale client

`wanted_names` never read its `previous` argument — the caller reassigns
`wanted` from the return value — so the parameter goes rather than gaining
an underscore; its one call site and four test calls follow. Sorts the
imports in test_artifacts.py. Both were failing `make lint-backend` at HEAD.

Regenerates the client, which 8cb843e left behind when it corrected the
revoke_client docstring.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CL9zvnnvcp1mvA8o7impxk

backend/tests/test_artifacts.py

@@ -7,7 +7,6 @@ from fastapi.testclient import TestClient
 from sqlmodel import Session, col, select
 
 from fluksio.core.config import settings
-
 from fluksio.core.db import engine as db_engine
 from fluksio.flow.artifacts import ArtifactStore, VolatileStore
 from fluksio.flow.runs import new_run_id, sweep_artifacts