Raise diff coverage above target by exercising the previously untested
lines:
- test_cli.py: invoke the `api` command with uvicorn.run mocked to assert
the default path passes the app object (no workers/factory) and that
--workers / API_WORKERS launches the env factory by import string with
the requested worker count and factory=True.
- test_app_factory.py: add METRICS_ENABLED true/false cases that toggle
the /metrics route, covering the env-bool parsing branch.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>