[FEATURE]: Add Bookmark / Save Favorite Books #537

Feature Summary

Add a Bookmark / Save Favorite Books feature that allows users to save their preferred books or entries and access them later in a dedicated Favorites/Bookmarks section. This improves usability and personalization of the Bibliodrift platform.

Problem Statement

Currently, users have no way to save or mark books they are interested in. If a user wants to revisit a previously viewed book, they must manually search or scroll again, which reduces user experience and engagement. There is no persistence mechanism for favorite content.

Proposed Solution

Implement a Bookmark feature using a simple toggle system on each book card:

Add a ⭐ Bookmark icon/button on each book/entry card
On click, toggle saved/unsaved state
Store bookmarked items in localStorage (MVP approach)
Create a dedicated “Bookmarks / Favorites” page or section
Display all saved books in a clean grid/list UI
Allow users to remove items from bookmarks easily
Ensure data persists after page refresh

Alternatives Considered

Using backend database storage for bookmarks
→ Rejected for MVP due to added complexity and authentication requirements
Session-based storage
→ Not suitable because data would be lost after browser close
External bookmarking tools
→ Not integrated and breaks user experience inside the app

Additional Context

This feature should be lightweight and frontend-first (localStorage-based MVP)
UI should match existing Bibliodrift design system
Must be fully responsive for mobile and desktop
Future enhancement can include backend sync + user accounts for persistent bookmarks across devices
Could later evolve into a recommendation system based on saved books