test(mcp): import only User locally; UserRole comes from the enclosing scope (#5035)

The local import shadowed UserRole for the whole function, so its earlier
use read an unassigned name (ruff F823, CI run 8294).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/integration/test_mcp_plugin_tools.py

@@ -255,7 +255,7 @@ def test_docker_and_agent_tools_over_seeded_rows(app):
 
         # ── the web pages say the same ─────────────────────────────────────
         # A real viewer: every request re-reads the session's user (refresh_session_user).
-        from steward.models.users import User, UserRole
+        from steward.models.users import User
         viewer_id = str(uuid.uuid4())
         async with app.db_sessionmaker() as s, s.begin():
             s.add(User(id=viewer_id, username=f"viewer-{viewer_id[:8]}", email=f"{viewer_id}@test",