fix(slack): delete stale progress messages

[Trantor-develops]

Summary\n- implement SlackAdapter.delete_message via chat.delete so cleanup_progress can remove temporary Working/tool-progress bubbles after the final response lands\n- treat Slack ok=false responses as best-effort cleanup failures instead of successful deletion\n- add Slack adapter tests plus a Slack-specific gateway cleanup_progress regression test\n\n## Verification\n- /Users/virtualmachine/.hermes/hermes-agent/.venv/bin/python -m pytest tests/gateway/test_slack.py tests/gateway/test_run_cleanup_progress.py -q -o 'addopts='\n - 227 passed, 38 existing AsyncMock warnings\n\n## Operational note\n- Slack chat.delete uses the existing chat:write bot scope for messages posted by the bot; no manifest/scope change required. Gateway restart is still required for the live adapter/config change to take effect.

[teknium1]

Thanks for the focused Slack cleanup implementation. Current main confirms the premise: gateway/run.py:17505-17511 disables cleanup_progress when an adapter inherits the no-op BasePlatformAdapter.delete_message implementation (gateway/platforms/base.py:3005-3024), and Slack has no override. The shared path already tracks successful progress-message IDs (gateway/run.py:17899-17915) and deletes them after final delivery (gateway/run.py:20371-20413).

The proposed Slack call follows the existing workspace-aware client resolution in plugins/platforms/slack/adapter.py:1379-1386; the added direct adapter tests cover success, workspace selection, disconnection, exceptions, and ok: false responses.

Automated hermes-sweeper review.

[teknium1]

Merged via #70189 — your commit was cherry-picked/reapplied onto current main with your authorship preserved in git history: your stale-progress deletion was cherry-picked.

Thanks for the contribution!