feat: Compact tree mode (tree + grid)

Currently tree is printed with a file entry per line, which scrolls quickly for a huge trees. But a lot of space on the right of screen is unused.

It would be useful if tree have a mode similar to a grid - with multiple files shown in a row.

With this it will be much easier for a user to understand structure of huge trees. (I even believe this should be a default and old, entry per line, mode is enabled by `-1`.

I think it may work if each leaf entry is appended to the row of a previous leaf entry or same level. With non-leaf entry (or new level) starts new line as usual.

Start by tracing how tree output is rendered and how the existing `-1` option selects the one-entry-per-line mode. Compare the current tree output with the requested grid behavior, including leaf entries, level changes, and non-leaf entries. Done means huge trees can show multiple leaf files per row while preserving the proposed `-1` mode.

Written by the indexing model from the issue text.