Add core chatbot module and CLI interface

[HeiligerHoly]

Summary

• extract reusable chatbot core logic for prediction and responses
• update the Tkinter GUI to use the shared chatbot utilities
• add a command line interface and README instructions for using the chatbot from the terminal

Testing

• Not run (nltk dependency unavailable in the execution environment)

---

Codex Task

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[chatgpt-codex-connector]

Avoid Python 3.10-only type syntax in Chatbot init

The new Chatbot constructor uses the PEP604 union operator (str | Path, str | None) introduced in Python 3.10. The README still points users to keras 2.2.0 (the error guide) which only supports Python ≤3.6, so following the documented setup and running python chatgui.py or python chatbot_cli.py on that environment will raise a SyntaxError before the app starts. Consider reverting to typing.Union/Optional (or bumping the documented Python version) so the chatbot remains runnable on the advertised stack.

Useful? React with 👍 / 👎.