fix: provide unique descriptions for /quit and /exit commands

[Marve10s]

Problem

The /quit and /exit commands in the help menu and autocomplete suggestions both display the identical description "exit Codex", making it unclear to users why two separate commands exist.

Solution

Updated the command definitions to provide unique, descriptive strings for each:

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[github-actions]

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[Marve10s]

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[etraut-openai]

These are aliases for the same command. They have the same description by design. For that reason, we're going to pass on this PR.