feat: show listing of terms added in Book or page #588

[marcomachado]

This PR implements a feature allowing users to view, search, and filter terms matching specific books and pages in the Term Index listing.

It satisfies the requirement to filter terms in 3 distinct modes:

1. Generic View (Terms -> Terms menu link): Opens with reset filters, hiding book scope controls;
2. Reading Page -> Term List: Opens showing terms from the current page, displaying book scope and page selectors;
3. Book Action List -> Terms: Opens with the current book selected;

Fixes #588

Changes

1. Backend Controllers & API

routes.py

• Updated /term/index to fetch all books, page counts, and current pages, serializing it to the template as books_json.
• Added a POST route /term/mark_current_page/<int:bookid>/<int:pagenum> to update a book's current page position.

2. Query Optimization

datatables.py

• Implemented book and page queries inside get_data_tables_list
• Refactored logic into helper functions to resolve pylint warnings (too many local variables, too many statements/branches).

3. UI Template

index.html

• Added Book, Page Scope, and Page number controls in the filter panels.
• Added Javascript logic to dynamically update options, keep state variables clean, and toggle scope visibility depending on URL parameters.

tablelisting.html

• Added a direct "Terms" link to the book listing actions dropdown.