feat: Display duplicate badges and enable deletion

Created by: Edouard-Legoupil

This commit addresses two issues related to duplicate knowledge cards:

1. Duplicate Badge Display: The "duplicate" badge was not appearing on all relevant cards. This was resolved by:

   • Replacing unstable array indices with unique IDs for the key prop in the Dashboard.jsx rendering loops. This ensures React can correctly track and re-render components.
   • Correcting the CSS for the .duplicate-badge and .delete-button to be positioned relative to their parent .card component, ensuring they appear within each card instead of stacking in a single spot.

2. Delete Functionality: Clicking the delete button on a duplicate card resulted in a 405 Method Not Allowed error. This was fixed by implementing the DELETE /knowledge-cards/{card_id} endpoint in the backend (backend/api/knowledge.py), which properly handles the deletion of a knowledge card and its associations.

A console.log has also been added to Dashboard.jsx to help with further debugging if needed.

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