Fix mac onboarding clean install path

[gateway]

Summary

• makes bootstrap_local.sh compatible with default macOS Bash 3 by removing associative arrays
• leaves Local OpenAI blank until the user opts into that provider
• cleans setup summary wording so skipped providers show Not set up without escaped spaces

Validation

• ran mac onboarding from a clean temp2 checkout in offline/no-launch mode
• bash -n scripts/bootstrap_local.sh scripts/onboard_mac.sh scripts/onboard_linux.sh
• git diff --check
• ./scripts/with_shared_python.sh -m pytest apps/api/tests/test_api_smoke.py::test_health_endpoint apps/api/tests/test_api_smoke.py::test_health_endpoint_reports_paused_when_queue_disabled -q