PR #14746: fix(gateway): default Slack tool_progress to off

• Repository: NousResearch/hermes-agent
• Author: xnbi
• State: open | merged: False
• Link: https://github.com/NousResearch/hermes-agent/pull/14746

Description (problem / solution / changelog)

Summary

Slack (Bolt / Socket Mode) cannot treat tool progress like the CLI spinner: each progress line becomes a permanent channel message. The previous built-in default (new via _TIER_MEDIUM) still emitted a line on every distinct tool start, which cluttered public channels (see #14663).

This PR sets the built-in Slack default to tool_progress: "off". Other tier-2 platforms (Mattermost, Matrix, Feishu) are unchanged. Users who want progress in Slack can still enable it globally, per-platform under display.platforms.slack, or cycle with /verbose when display.tool_progress_command is true.

Changes

• gateway/display_config.py: Slack uses {**_TIER_MEDIUM, "tool_progress": "off"} with a short comment referencing #14663.
• tests/gateway/test_display_config.py: Split Slack from the “medium tier = new” assertion; add test_slack_defaults_tool_progress_off. Migration tests now read/write config.yaml with encoding="utf-8" so they pass on Windows default locale (GBK).
• tests/gateway/test_verbose_command.py: /verbose isolation test expects Slack’s first cycle to go off → new instead of new → all.

Testing

pytest tests/gateway/test_display_config.py tests/gateway/test_verbose_command.py -q

## Changed files

- `gateway/display_config.py` (modified, +3/-1)
- `tests/gateway/test_display_config.py` (modified, +12/-6)
- `tests/gateway/test_verbose_command.py` (modified, +3/-3)