Feature/chat settings invoke

[Barani05072002]

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Title: Add Chat Settings Invocation via @ Keyword (#2850)

Hello friends. I saw one of the feature enhancement issue in chainlit repo #2580. PR introduces a new way for users to invoke chat settings using the '@' keyword. The feature enhances input interaction by supporting both '@' and '/' triggers:

• Typing @ now displays the chat settings input prompt.
• Typing / continues to show input values as before.
• This dual-trigger approach improves accessibility and flexibility for users interacting with chat settings.

All relevant UI and backend logic have been updated to support this behavior.

Let me know if you'd like to add screenshots to related issues or discussions from the [#2580].

Thanks.