Feature: preview mode

Before entering a folder, the user would be able to press "p" in order to see a preview of the folder.

This preview would appear on the folder's tile itself instead of the folder name and size, and would contain a nested map of the folder itself. The user would not be able to select any of the rectangles within though - for that they would have to press "ENTER" as usual and enter it.

No files, tests, or entry points are named. Start by locating the terminal folder-navigation and tile-rendering code, then confirm the interaction and rendering design with maintainers. Done means pressing "p" shows a non-selectable nested folder map on the tile, while ENTER still enters the folder normally.

Written by the indexing model from the issue text.