Display deprecation message when run from command line

[mentatai]

When the old CLI version is run, display a message informing users that this project is deprecated and directing them to mentat.ai for the current version of Mentat.

Closes #592

🤖 See my steps and track the cost of the PR here ✨

[mentatai]

I've modified the run_cli() function to display a deprecation message instead of starting the terminal client. When users try to run the old CLI version, they'll now see:

1. A clear warning that this version is deprecated
2. Information about the new Mentat project
3. A link to mentat.ai where they can find the current version
4. A reference to @AbanteAI on Twitter for questions

The program exits with status code 1 to indicate this is an error condition, which should help prevent any scripts from silently continuing with the deprecated version.

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