Add Average h-index by research field

[sabrinek8]

I added:

1. New "Research Fields" tab between "Author Table" and "Chat"
2. Simple, focused display showing: - Summary metrics (total authors, fields, highest avg h-index, most popular field) - Main table of research fields ranked by average H-Index - Filters for minimum authors and number of fields to show - Field details showing all authors in a selected research field

Note: I recommend adding encoding='utf-8' to properly handle French characters and other special characters in your data