WIP Podgląd zawartości elementów listy

Dodać możliwość podglądu złaczanych plików (tekstów).
* Po kliknięciu na elementy **[listy z tekstami do dodania]** oraz z **[listy z tekstami do usunięcia]**:

The issue names the list of texts to add and the list of texts to remove, but no files or tests. Start by locating the UI entry point that renders these lists and inspect how their items are handled on click. Done means clicking an item provides a preview of the corresponding text file in both lists.

Written by the indexing model from the issue text.