Default Slack tool progress to off

[mosabbirrakib]

Summary

• default Slack gateway tool progress to off so Slack chats stay quiet by default
• keep other medium-tier platforms unchanged
• update gateway tests for the quieter Slack default and explicitly opt into progress where the Slack threading test needs it

Testing

• source venv/bin/activate && python -m pytest tests/gateway/test_display_config.py tests/gateway/test_verbose_command.py tests/gateway/test_run_progress_topics.py::test_run_agent_progress_uses_event_message_id_for_slack_dm -q

[teknium1]

Closing as superseded by #70189 (merged): the lifecycle fixes landed via #70189; your default-off proposal is a behavior-default change held for an explicit maintainer decision — it may still land separately.

Thanks for the work — it's credited in #70189's summary.