Should be possible to set the tabstop size

**Is your feature request related to a problem? Please describe.**
It shows patches with a smaller tab space (4) than it should be (8).
There is a tabs(1) command: "The tabs program clears and sets tab-stops on the terminal."
But it has no effect on gitui.

**Describe the solution you'd like**
gitui should use either an environment variable or a config setting, or it should respect what the tabs(1) command sets.

**Additional context**
FreeBSD 14.0

The issue names no files, tests, or entry points. Start by locating gitui's terminal rendering and configuration code, then determine how tab stops should be configured or inherited from the terminal; done means patches render with the requested tab width on FreeBSD.

Written by the indexing model from the issue text.