fix: coping text from dark mode shouldn't keep the colors

[adoxentor]

Summary

When copying text from an answer in dark mode, the copied content retains the dark mode styling (light text on dark background) when pasted into other applications like Google Docs.
This is unlike other writing assistance platforms, such as ChatGPT, which have implemented a fix for this issue.
This fix registers a copy event listener that removes the styling from the text.
Fixes: #3954

Change Type

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• Bug fix

Testing

Just copy a message from the bot that has formatting into Google Docs.

Test Configuration:

Checklist

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• My code adheres to this project's style guidelines
• I have performed a self-review of my own code
• I have commented in any complex areas of my code
• My changes do not introduce new warnings