Replace non-existent `gt mail ack` with `gt mail delete` in the witness
role template. The `ack` subcommand exists in `bd mail` but not in
`gt mail` - the correct command is `gt mail delete` which acknowledges
and closes messages.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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