fix(slack): normalize typed command mentions

[Pumpurri]

Context

Fixes #315

Slack encodes an autocomplete-selected mention as <@U123>, even though it displays the mention as @username in the client.

The Slack slash-command path normalizes this encoding with translate_inbound, but the typed !command path previously passed its arguments to the command dispatcher unchanged. As a result, commands such as !invite-agent could silently fail when their target was selected from Slack’s autocomplete popup.

Description

Normalize typed Slack !command arguments using translate_inbound before dispatching them.

This converts Slack-encoded mentions such as <@U123> into the @username format expected by the command dispatcher. The stale slash-command comment was also updated to describe the shared normalization behavior accurately.

The related adapters were checked in the same pass:

• Discord already normalizes typed-command mentions and has regression coverage.
• Mattermost sends mentions as literal @username, so no normalization change is required.

Steps to review

• core/switch_core/bridges/collaboration/slack/adapter.py — confirm typed command arguments pass through translate_inbound.
• core/tests/switch_core/bridges/collaboration/test_slack_adapter.py — regression test sends !invite-agent <@U999> and verifies the dispatcher receives @worker.
• Confirm the slash-command path continues using the same inbound translation.

Tests:

• just check — passed
• just typecheck — passed
• just test — 2011 passed, 5 deselected
• Live Slack test — an autocomplete-selected mention in !invite-agent @username successfully added the corresponding Switch agent

[github-actions]

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[Pumpurri]

I have read the CLA Document and I hereby sign the CLA

[amaudruz]

Nice, thanks for this !