Library: Refactor instructions to use unique book IDs using crypto.randomUUID() instead of array indices

[dekr1sh]

Because

This PR updates the project instructions to recommend using unique book IDs using crypto.randomUUID() instead of array indices for identifying books in the library. This change improves the stability and maintainability of the code by ensuring each book has a consistent identifier, even when books are added or removed.

This PR

• Updated project instructions to use unique book IDs instead of array indices.
• Clarified the benefits of using unique IDs for stability and maintainability.
• Added a link to MDN documentation on data attributes, which was not included previously.

Issue

Closes #29341

Additional Information

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