Handle before unload event for chat mode

[rishabh8870]

Add beforeunload event listener to warn users when closing tab during active chat

Description

This PR implements a warning dialog when users attempt to close the browser tab while actively chatting (on the /founduser route). This prevents accidental data loss and provides a better user experience.

Changes Proposed

• Added a beforeunload event listener in the App component
• The listener checks if the user is on the /founduser route (active chat)
• If in chat mode, it prevents the default unload and shows the browser's confirmation dialog
• Properly cleans up the event listener on component unmount

How to Test

1. Start a chat with another user (navigate to /founduser)
2. Try to close the browser tab or navigate away
3. A browser confirmation dialog should appear
4. Click Cancel to stay in chat, or Leave to close

Fixes issue #452

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[github-actions]

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[Dun-sin]

Your pull request is rejected, reason 👉🏾is here👈🏾

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